Detect warning options during configure

Certain options maybe compiler specific therefore its better
to detect them before use.

nfs_error copies the format string and appends newline to it
but compiler can forget that it was format string since its not
same fmt string that was passed. Ignore the warning

Wdiscarded-qualifiers is gcc specific and this is no longer needed

Upstream-Status: Pending
Signed-off-by: Khem Raj <raj.khem@gmail.com>

--- a/configure.ac
+++ b/configure.ac
@@ -599,7 +599,6 @@ my_am_cflags="\
  -Werror=parentheses \
  -Werror=aggregate-return \
  -Werror=unused-result \
- -Wno-cast-function-type \
  -fno-strict-aliasing \
 "
 
@@ -619,9 +618,10 @@ CHECK_CCSUPPORT([-Werror=format-overflow
 CHECK_CCSUPPORT([-Werror=int-conversion], [flg2])
 CHECK_CCSUPPORT([-Werror=incompatible-pointer-types], [flg3])
 CHECK_CCSUPPORT([-Werror=misleading-indentation], [flg4])
+CHECK_CCSUPPORT([-Wno-cast-function-type], [flg5])
 AX_GCC_FUNC_ATTRIBUTE([format])
 
-AC_SUBST([AM_CFLAGS], ["$my_am_cflags $flg1 $flg2 $flg3 $flg4"])
+AC_SUBST([AM_CFLAGS], ["$my_am_cflags $flg1 $flg2 $flg3 $flg4 $flg5"])
 
 # Make sure that $ACLOCAL_FLAGS are used during a rebuild
 AC_SUBST([ACLOCAL_AMFLAGS], ["-I $ac_macro_dir \$(ACLOCAL_FLAGS)"])
--- a/support/nfs/xcommon.c
+++ b/support/nfs/xcommon.c
@@ -98,7 +98,10 @@ nfs_error (const char *fmt, ...) {
 
      fmt2 = xstrconcat2 (fmt, "\n");
      va_start (args, fmt);
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wformat-nonliteral"
      vfprintf (stderr, fmt2, args);
+#pragma GCC diagnostic pop
      va_end (args);
      free (fmt2);
 }
--- a/utils/mount/stropts.c
+++ b/utils/mount/stropts.c
@@ -1094,9 +1094,7 @@ static int nfsmount_fg(struct nfsmount_i
 		if (nfs_try_mount(mi))
 			return EX_SUCCESS;
 
-#pragma GCC diagnostic ignored "-Wdiscarded-qualifiers"
 		if (errno == EBUSY && is_mountpoint(mi->node)) {
-#pragma GCC diagnostic warning "-Wdiscarded-qualifiers"
 			/*
 			 * EBUSY can happen when mounting a filesystem that
 			 * is already mounted or when the context= are