Avoid implicit declaration of the exit and strcmp functions.  Improves
compatibility with C99 compilers.

diff -ur grace-5.1.25.orig/ac-tools/aclocal.m4 grace-5.1.25/ac-tools/aclocal.m4
--- grace-5.1.25.orig/ac-tools/aclocal.m4	2022-12-22 10:27:28.504523927 +0100
+++ grace-5.1.25/ac-tools/aclocal.m4	2022-12-22 10:30:25.072665840 +0100
@@ -51,7 +51,7 @@
       unsigned int B = 3;
       int i;
       for(i=0; i<B; i++) Array[[i]] = i - 3;
-      exit( Array[[1]] != -2 );
+      return Array[[1]] != -2;
     }
     ],
 
@@ -105,7 +105,7 @@
       	}
     }
  
-    exit(i);
+    return i;
 }],
     ac_cv_c_fpu_arithmetics_type="Unknown",
     [case "$?" in
@@ -282,12 +282,12 @@
         vincn = XmVersion;
         vlibn = xmUseVersion;
         if (vincn < [$1]) {
-          exit(1);
+          return 1;
         }
         if (vincn != vlibn) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -373,9 +373,9 @@
         char *vlib;
         vlib = T1_GetLibIdent();
         if (strcmp(vlib, "[$1]") < 0) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -419,12 +419,12 @@
         vlib = zlibVersion();
         vinc = ZLIB_VERSION;
         if (strcmp(vinc, "[$1]") < 0) {
-          exit(1);
+          return 1;
         }
         if (strcmp(vinc, vlib) != 0) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -469,9 +469,9 @@
         jpeg_create_compress(&cinfo);
         vinc = JPEG_LIB_VERSION;
         if (vinc < [$1]) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -515,12 +515,12 @@
         vlib = png_libpng_ver;
         vinc = PNG_LIBPNG_VER_STRING;
         if (strcmp(vinc, "[$1]") < 0) {
-          exit(1);
+          return 1;
         }
         if (strcmp(vinc, vlib) != 0) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -565,12 +565,12 @@
         vincn = 100*PDFLIB_MAJORVERSION + PDFLIB_MINORVERSION;
         vinc = PDFLIB_VERSIONSTRING;
         if (strcmp(vinc, "[$1]") < 0) {
-          exit(1);
+          return 1;
         }
         if (vincn != vlibn) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -611,13 +611,14 @@
     AC_TRY_RUN([
 #include <stdio.h>
 #include <netcdf.h>
+#include <string.h>
       int main(void) {
         char *vlib;
         vlib = nc_inq_libvers();
         if (strcmp(vlib, "[$1]") < 0) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -659,9 +660,9 @@
       int main(void) {
         char *vlib = (char *) fftw_version;
         if (strcmp(vlib, "[$1]") < 0) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
       ],
 
@@ -706,12 +707,12 @@
         vlib = XmHTMLGetVersion();
         vinc = XmHTMLVersion;
         if (vinc < [$1]) {
-          exit(1);
+          return 1;
         }
         if (vinc != vlib) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
       ],
 
diff -ur grace-5.1.25.orig/configure grace-5.1.25/configure
--- grace-5.1.25.orig/configure	2022-12-22 10:27:28.505523916 +0100
+++ grace-5.1.25/configure	2022-12-22 10:32:18.581471350 +0100
@@ -4242,7 +4242,7 @@
       unsigned int B = 3;
       int i;
       for(i=0; i<B; i++) Array[i] = i - 3;
-      exit( Array[1] != -2 );
+      return Array[1] != -2;
     }
 
 _ACEOF
@@ -4964,7 +4964,7 @@
       	}
     }
 
-    exit(i);
+    return i;
 }
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :
@@ -7808,9 +7808,9 @@
         char *vlib;
         vlib = T1_GetLibIdent();
         if (strcmp(vlib, "1.3.1") < 0) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -8181,13 +8181,14 @@
 
 #include <stdio.h>
 #include <netcdf.h>
+#include <string.h>
       int main(void) {
         char *vlib;
         vlib = nc_inq_libvers();
-        if (((vlib[0] == '"') && (strcmp(vlib, "\"3.0") < 0)) || ((vlib[0] != '"') && (strcmp(vlib, "3.0") < 0))){
-          exit(1);
+        if (strcmp(vlib, "3.0") < 0) {
+          return 1;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -8267,9 +8268,9 @@
       int main(void) {
         char *vlib = (char *) fftw_version;
         if (strcmp(vlib, "2.1.3") < 0) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -8352,12 +8353,12 @@
         vlib = zlibVersion();
         vinc = ZLIB_VERSION;
         if (strcmp(vinc, "1.0.3") < 0) {
-          exit(1);
+          return 1;
         }
         if (strcmp(vinc, vlib) != 0) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -8438,9 +8439,9 @@
         jpeg_create_compress(&cinfo);
         vinc = JPEG_LIB_VERSION;
         if (vinc < 61) {
-          exit(1);
+          return 1;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -8522,12 +8523,12 @@
         vlib = png_libpng_ver;
         vinc = PNG_LIBPNG_VER_STRING;
         if (strcmp(vinc, "0.9.6") < 0) {
-          exit(1);
+          return 1;
         }
         if (strcmp(vinc, vlib) != 0) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -8610,12 +8611,12 @@
         vincn = 100*PDFLIB_MAJORVERSION + PDFLIB_MINORVERSION;
         vinc = PDFLIB_VERSIONSTRING;
         if (strcmp(vinc, "5.0.0") < 0) {
-          exit(1);
+          return 1;
         }
         if (vincn != vlibn) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -9558,12 +9559,12 @@
         vincn = XmVersion;
         vlibn = xmUseVersion;
         if (vincn < 1002) {
-          exit(1);
+          return 1;
         }
         if (vincn != vlibn) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF
@@ -9830,12 +9831,12 @@
         vlib = XmHTMLGetVersion();
         vinc = XmHTMLVersion;
         if (vinc < 1105) {
-          exit(1);
+          return 1;
         }
         if (vinc != vlib) {
-          exit(2);
+          return 2;
         }
-        exit(0);
+        return 0;
       }
 
 _ACEOF