Fix Github Actions for macos system update (CICE-Consortium#948)

Github Actions broke again after default macos system update.

Clang was not picking up the C system files. Had to change the implementation and add -isysroot to the CFLAGS option. At the same time, removed prior implementation where the system files were linked into /usr/local/include, this was no longer working.

.github/workflows/test-cice.yml

@@ -46,7 +46,6 @@ jobs:
         run: |
           sudo xcode-select -r
           sudo xcode-select -s /Library/Developer/CommandLineTools
-          sudo ln -s /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/* /usr/local/include/
           echo "xcrun --show-sdk-path: $(xcrun --show-sdk-path)"
           echo "xcode-select -p: $(xcode-select -p)"
       - name: system info
@@ -55,7 +54,7 @@ jobs:
           type wget
           type curl
           type csh
-          echo "readlink \$(which csh): $(python -c 'import os, sys; print os.path.realpath(sys.argv[1])' $(which csh))"
+          echo "readlink \$(which csh): $(python -c 'import os, sys; print(os.path.realpath(sys.argv[1]))' $(which csh))"
           echo "csh --version: $(csh --version)"
           echo "uname -a: $(uname -a)"
           echo "sw_vers: $(sw_vers)"

configuration/scripts/machines/Macros.conda_macos

@@ -47,7 +47,8 @@ SDKPATH = $(shell xcrun --show-sdk-path)
 ifeq ($(strip $(SDKPATH)),)
   CFLAGS_HOST := 
 else
-  CFLAGS_HOST = -isysroot $(SDKPATH)
+  CFLAGS_HOST := -isysroot $(SDKPATH)
+  CFLAGS += -isysroot $(SDKPATH)
   LD += -L$(SDKPATH)/usr/lib
 endif