[NO REVIEW] CI: Add Linux/ARM64 coverage for flang 23 RC3

.github/workflows/build.yml

@@ -112,6 +112,11 @@ jobs:
             #container: snowstep/llvm:debian-12-latest
 
           # https://hub.docker.com/r/phhargrove/llvm-flang/tags
+          - os: ubuntu-26.04-arm
+            compiler: flang
+            version: 23
+            container: phhargrove/llvm-flang:23.1.0_rc3-latest-arm64
+
           - os: ubuntu-24.04
             compiler: flang
             version: 23
@@ -225,6 +230,11 @@ jobs:
             version: 22
             network: udp
             container: phhargrove/llvm-flang:22.1.0-latest
+          - os: ubuntu-26.04-arm
+            compiler: flang
+            network: udp
+            version: 23
+            container: phhargrove/llvm-flang:23.1.0_rc3-latest-arm64
           - os: ubuntu-24.04
             compiler: flang
             version: 23

install.sh

@@ -600,6 +600,7 @@ elif echo "build test run install" | grep -w -q -e "\$fpm_sub_cmd" ; then
   "\$@"
 elif echo "set-native" | grep -w -q -e "\$fpm_sub_cmd" ; then
   set -e
+  mkdir -p build
   cmd="\$FC \$RAWFLAGS app/print-native-flags.F90 -o build/print-native-flags $APPEND_LDFLAGS"
   eval \$cmd || (set -x ; eval \$cmd)
   NATIVEFLAGS="\`build/print-native-flags\`"