Skip gcc15 for Ubuntu until available, workaround GCC 15.1 bug

Author: krystophny

.github/workflows/CI.yml

@@ -30,6 +30,8 @@ jobs:
           - {compiler: gcc, version: 15}
           - {compiler: intel, version: 2025.1}
         exclude:
+          - os: ubuntu-latest  # gcc 15 not available on Ubuntu yet
+            toolchain: {compiler: gcc, version: 15}
           - os: macos-13  # No Intel on MacOS anymore since 2024
             toolchain: {compiler: intel, version: '2025.1'}
           - os: windows-latest  # Doesn't pass build and tests yet

src/fpm_compiler.F90

@@ -178,7 +178,7 @@ module fpm_compiler
     flag_gnu_opt = " -O3 -funroll-loops", &
     flag_gnu_debug = " -g", &
     flag_gnu_pic = " -fPIC", &
-    flag_gnu_warn = " -Wall -Wextra", &
+    flag_gnu_warn = " -Wall -Wextra -Wnoexternal-argument-mismatch", &
     flag_gnu_check = " -fcheck=bounds -fcheck=array-temps", &
     flag_gnu_limit = " -fmax-errors=1", &
     flag_gnu_external = " -Wimplicit-interface", &