Improve C99 compatibility of code-generating shell scripts

Explicitly declare the int return type of the main function.  This
improves compatibility with future C99-only compilers, which might
no longer support implicit ints.

Submitted upstream: <https://github.com/kmatheussen/jack_capture/pull/52>

diff --git a/gen_das_config_h.sh b/gen_das_config_h.sh
index a8c3c3377c4ad6f7..8739cf9e527672df 100644
--- a/gen_das_config_h.sh
+++ b/gen_das_config_h.sh
@@ -14,7 +14,7 @@
 
 
 echo "#include <sndfile.h>" >temp$$.c
-echo "main(){return SF_FORMAT_OGG;}" >>temp$$.c
+echo "int main(void){return SF_FORMAT_OGG;}" >>temp$$.c
 echo >>temp$$.c
 if gcc temp$$.c 2>/dev/null; then
     echo "#define HAVE_OGG 1"
@@ -24,7 +24,7 @@ fi
 
 
 echo "#include <lame/lame.h>" >temp$$.c
-echo "main(){return 0;}" >>temp$$.c
+echo "int main(void){return 0;}" >>temp$$.c
 echo >>temp$$.c
 if gcc temp$$.c -lmp3lame 2>/dev/null; then
     echo "#define HAVE_LAME 1"
@@ -35,7 +35,7 @@ fi
 
 
 echo "#include <lo/lo.h>" >temp$$.c
-echo "main(){return 0;}" >>temp$$.c
+echo "int main(void){return 0;}" >>temp$$.c
 echo >>temp$$.c
 if pkg-config --cflags --libs liblo >/dev/null 2>/dev/null && gcc temp$$.c `pkg-config --cflags --libs liblo` 2>/dev/null ; then
     echo "#define HAVE_LIBLO 1"
@@ -46,7 +46,7 @@ fi
 
 
 echo "#include <jack/jack.h>" >temp$$.c
-echo "main(){return (int)jack_port_get_latency_range;}" >>temp$$.c
+echo "int main(void){return (int)jack_port_get_latency_range;}" >>temp$$.c
 echo >>temp$$.c
 if gcc temp$$.c -ljack 2>/dev/null ; then
     echo "#define NEW_JACK_LATENCY_API 1"
diff --git a/gen_setformat_c.sh b/gen_setformat_c.sh
index 2202df2495005b75..c255157df2ab7281 100644
--- a/gen_setformat_c.sh
+++ b/gen_setformat_c.sh
@@ -55,7 +55,7 @@ echo "  return("
 
 for a in $ai;do
     echo "#include <sndfile.h>" >temp.c
-    echo "main(){return SF_FORMAT_"$a";}" >>temp.c
+    echo "int main(void){return SF_FORMAT_"$a";}" >>temp.c
     echo >>temp.c
     if gcc temp.c 2>/dev/null; then
 	echo "    (!strcasecmp(\""$a"\",soundfile_format)) ? SF_FORMAT_"$a":"