--- make/autoconf/flags-cflags.m4~	Wed Apr  8 19:47:07 2020
+++ make/autoconf/flags-cflags.m4	Thu Apr  9 17:26:51 2020
@@ -539,8 +539,8 @@
   fi
 
   if test "x$TOOLCHAIN_TYPE" = xgcc; then
-    TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -fcheck-new -fstack-protector"
-    TOOLCHAIN_CFLAGS_JDK="-pipe -fstack-protector"
+    TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -fcheck-new"
+    TOOLCHAIN_CFLAGS_JDK="-pipe"
     # reduce lib size on s390x in link step, this needs also special compile flags
     if test "x$OPENJDK_TARGET_CPU" = xs390x; then
       TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -ffunction-sections -fdata-sections"
--- make/autoconf/flags-cflags.m4~	Wed Jan 21 13:16:25 2026
+++ make/autoconf/flags-cflags.m4	Wed Jan 21 13:38:22 2026
@@ -600,7 +600,7 @@
   if test "x$TOOLCHAIN_TYPE" = xgcc || test "x$TOOLCHAIN_TYPE" = xclang || test "x$TOOLCHAIN_TYPE" = xxlc; then
     # This raises the language level for older 4.8 gcc, while lowering it for later
     # versions. clang and xlclang support the same flag.
-    LANGSTD_CFLAGS="-std=c99"
+    LANGSTD_CFLAGS="-std=gnu99"
   elif test "x$TOOLCHAIN_TYPE" = xsolstudio; then
     # We can't turn on -std=c99 without breaking compilation of the splashscreen/png
     # utilities. But we can enable c99 as below (previously achieved by using -Xa).