use AC_PROG_CC_C99 to find flags to turn on c99 support. remove if mtt fails because of this.

This commit was SVN r24291.

configure.ac

@@ -468,6 +468,8 @@ if test "x$CC" = "xicc"; then
     OMPI_CHECK_ICC_VARARGS
 fi
 
+AC_PROG_CC_C99
+
 # If we want the profiling layer:
 # - If the C compiler has weak symbols, use those.
 # - If not, then set to compile the code again with #define's in a