Use AC_USE_SYSTEM_EXTENSIONS to enable declarations of asprintf,
vasprintf in the glibc headers. Otherwise the corresponding configure
probes will fail with compilers that do not support implicit function
declarations by default.
Submitted upstream: <https://sourceforge.net/p/matio/patches/12/>
diff --git a/configure.ac b/configure.ac
index 7253c4f740c198e8..f9eb0dd9e1dae1cc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -53,6 +53,7 @@ dnl
dnl Build programs, C compiler, F77 compiler, make, install, etc.
dnl
AC_PROG_CC([pgcc icc gcc cc])
+AC_USE_SYSTEM_EXTENSIONS
AC_ARG_ENABLE(coverage,
[ --enable-coverage Enable coverage testing],