Build with -Werror on most recent gcc and clang.

.github/configs

@@ -29,6 +29,19 @@ case "$config" in
 	LIBCRYPTOFLAGS="--without-openssl"
 	TEST_TARGET=t-exec
 	;;
+   clang-12-Werror)
+	CC="clang-12"
+	# clang's implicit-fallthrough requires that the code be annotated with
+	# __attribute__((fallthrough)) and does not understand /* FALLTHROUGH */
+	CFLAGS="-Wall -Wextra -O2 -Wno-error=implicit-fallthrough"
+	CONFIGFLAGS="--with-pam --with-Werror"
+	;;
+    gcc-11-Werror)
+	CC="gcc"
+	# -Wnoformat-truncation in gcc 7.3.1 20180130 fails on fmt_scaled
+	CFLAGS="-Wall -Wextra -Wno-format-truncation -O2 -Wimplicit-fallthrough=4"
+	CONFIGFLAGS="--with-pam --with-Werror"
+	;;
     clang*|gcc*)
 	CC="$config"
 	;;

.github/workflows/c-cpp.yml

@@ -29,11 +29,11 @@ jobs:
           - { os: ubuntu-20.04, configs: clang-9 }
           - { os: ubuntu-20.04, configs: clang-10 }
           - { os: ubuntu-20.04, configs: clang-11 }
-          - { os: ubuntu-20.04, configs: clang-12 }
+          - { os: ubuntu-20.04, configs: clang-12-Werror }
           - { os: ubuntu-20.04, configs: gcc-7 }
           - { os: ubuntu-20.04, configs: gcc-8 }
           - { os: ubuntu-20.04, configs: gcc-10 }
-          - { os: ubuntu-20.04, configs: gcc-11 }
+          - { os: ubuntu-20.04, configs: gcc-11-Werror }
           - { os: ubuntu-20.04, configs: pam }
           - { os: ubuntu-20.04, configs: kitchensink }
           - { os: ubuntu-20.04, configs: hardenedmalloc }