configure: Check if "-D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600" is needed for localtime_r()

Fixes build with musl
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -4234,6 +4234,15 @@ probe_libc(){
         eval ${pfx}libc_type=solaris
         add_${pfx}cppflags -D__EXTENSIONS__ -D_XOPEN_SOURCE=600
     fi
+    check_${pfx}cc <<EOF
+#include <time.h>
+void *v = localtime_r;
+EOF
+test "$?" != 0 && check_${pfx}cc -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600 <<EOF && add_${pfx}cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
+#include <time.h>
+void *v = localtime_r;
+EOF
+
 }
 
 probe_libc