github: build with "-fexceptions" CFLAGS

This seems good for our test builds.

This can result in additional uninitialized variable warnings about
autovariables with cleanup attribute.

This flag is also enabled by default on Fedora package build ([1]).

[1] https://src.fedoraproject.org/rpms/redhat-rpm-config//blob/rawhide/f/buildflags.md

.github/workflows/ci.yml

@@ -70,7 +70,7 @@ jobs:
           set -x
 
           export CC="${{ matrix.cc }}"
-          export CFLAGS="-DNL_MORE_ASSERTS=1000 -O2 -Werror -Wall -Wdeclaration-after-statement -Wvla -std=gnu11"
+          export CFLAGS="-DNL_MORE_ASSERTS=1000 -O2 -Werror -Wall -Wdeclaration-after-statement -Wvla -std=gnu11 -fexceptions"
           if [ "$CC" = "clang" ]; then
                   CFLAGS="$CFLAGS -Wno-error=unused-command-line-argument -Wno-error=unused-function"
                   export LDFLAGS="-Wl,--no-undefined-version,--fatal-warnings"
@@ -128,7 +128,7 @@ jobs:
           set -x
           git clean -fdx
           export CC="${{ matrix.cc }}"
-          export CFLAGS="-Werror -Wall -Wdeclaration-after-statement -Wvla -std=gnu11"
+          export CFLAGS="-Werror -Wall -Wdeclaration-after-statement -Wvla -std=gnu11 -fexceptions"
           if [ "$CC" = "clang" ]; then
                   CFLAGS="$CFLAGS -Wno-error=unused-command-line-argument -Wno-error=unused-function"
           fi
@@ -188,7 +188,7 @@ jobs:
           set -x
 
           export CC="${{ matrix.cc }}"
-          export CFLAGS="-DNL_MORE_ASSERTS=1000 -O2 -Werror -Wall -Wdeclaration-after-statement -Wvla -std=gnu11"
+          export CFLAGS="-DNL_MORE_ASSERTS=1000 -O2 -Werror -Wall -Wdeclaration-after-statement -Wvla -std=gnu11 -fexceptions"
           if [ "$CC" = "clang" ]; then
                   CFLAGS="$CFLAGS -Wno-error=unused-command-line-argument -Wno-error=unused-function"
                   export LDFLAGS="-Wl,--no-undefined-version,--fatal-warnings"