build: enable GNU C99 extension by default (#5099)

Co-authored-by: Anton Kochkov <anton.kochkov@gmail.com>

Author: notxvilka

.github/workflows/ci.yml

@@ -368,7 +368,7 @@ jobs:
         working-directory: rizin
       - name: Build
         run: |
-          meson setup --prefix=/usr build && ninja -C build
+          meson setup -Dc_std=gnu99 --prefix=/usr build && ninja -C build
         working-directory: rizin
       - name: Install
         run: ninja -C build install
@@ -450,7 +450,7 @@ jobs:
         run: find subprojects -name '*.wrap' | xargs sed -i '/^depth = 1$/d'
         working-directory: rizin
       - name: Build with Meson + Ninja
-        run: meson setup --prefix=/usr build && ninja -C build
+        run: meson setup -Dc_std=gnu99 --prefix=/usr build && ninja -C build
         working-directory: rizin
       - name: Install with Ninja
         run: ninja -C build install

meson.build

@@ -5,7 +5,6 @@ project('rizin', 'c',
   default_options: [
     'buildtype=debugoptimized',
     'b_vscrt=from_buildtype',
-    'c_std=c99',
     'warning_level=1',
   ]
 )
@@ -91,6 +90,16 @@ if cc.has_argument('-Wenum-compare')
   add_project_arguments('-DCC_SUPPORTS_W_ENUM_COMPARE', language: ['c', 'cpp'])
 endif
 
+if cc.has_argument('-std=gnu99')
+  add_project_arguments('-std=gnu99', language: ['c', 'cpp'])
+elif cc.has_argument('--std=gnu99')
+  add_project_arguments('--std=gnu99', language: ['c', 'cpp'])
+elif cc.has_argument('-std=c99')
+  add_project_arguments('-std=c99', language: ['c', 'cpp'])
+elif cc.has_argument('--std=c99')
+  add_project_arguments('--std=c99', language: ['c', 'cpp'])
+endif
+
 # Sanitize correct usage of rz_strf()
 if cc.has_argument('-Werror=sizeof-pointer-memaccess')
   add_project_arguments('-Werror=sizeof-pointer-memaccess', language: ['c', 'cpp'])