meson, ci: Raise the minimum to C11 and use C17 or C23 if available

C11 has been available for 15 years now, and virtually all reasonable
C compilers support it. But we also want to opportunistically use
C17 or C23 as they are stricter, which helps us have better code.

This also adds test runs for the oldest standard supported.

Signed-off-by: Neal Gompa <neal@gompa.dev>

.gitlab-ci.yml

@@ -175,6 +175,11 @@ armv7-debian-container_prep:
   variables:
     MESON_BUILD_TYPE: "-Dbuildtype=release"
 
+.build-oldstd:
+  stage: "Other build configurations"
+  variables:
+    MESON_ARGS: "-Dc_std=c11"
+
 
 # OS/architecture-specific variants
 .build-env-debian-x86_64:
@@ -222,7 +227,7 @@ armv7-debian-container_prep:
     - .ci-rules
   stage: "Build and test"
   script:
-    - meson setup $BUILDDIR --prefix="$PREFIX" -Dicon_directory=/usr/share/X11/icons --fatal-meson-warnings -Dwerror=true ${MESON_BUILD_TYPE}
+    - meson setup $BUILDDIR --prefix="$PREFIX" -Dicon_directory=/usr/share/X11/icons --fatal-meson-warnings -Dwerror=true ${MESON_BUILD_TYPE} ${MESON_ARGS}
     - ninja -C $BUILDDIR -k0 -j${FDO_CI_CONCURRENT:-4}
     - meson test -C $BUILDDIR --num-processes ${FDO_CI_CONCURRENT:-4}
     - ninja -C $BUILDDIR clean
@@ -278,6 +283,12 @@ x86_64-release-debian-build:
     - .do-build
     - .build-release
 
+x86_64-oldstd-debian-build:
+  extends:
+    - .build-env-debian-x86_64
+    - .do-build
+    - .build-oldstd
+
 aarch64-debian-build:
   extends:
     - .build-env-debian-aarch64
@@ -289,6 +300,12 @@ aarch64-release-debian-build:
     - .do-build
     - .build-release
 
+aarch64-oldstd-debian-build:
+  extends:
+    - .build-env-debian-aarch64
+    - .do-build
+    - .build-oldstd
+
 armv7-debian-build:
   extends:
     - .build-env-debian-armv7
@@ -300,6 +317,12 @@ armv7-release-debian-build:
     - .do-build
     - .build-release
 
+armv7-oldstd-debian-build:
+  extends:
+    - .build-env-debian-armv7
+    - .do-build
+    - .build-oldstd
+
 # Base variables used for anything using a FreeBSD environment
 .os-freebsd:
   variables:

meson.build

@@ -6,7 +6,7 @@ project(
 	default_options: [
 		'warning_level=2',
 		'buildtype=debugoptimized',
-		'c_std=c99',
+		'c_std=' + (meson.version().version_compare('>=1.3.0') ? 'c23,c17,c11' : 'c11'),
 	]
 )