Fix MacOS Posix port (#957)

PR #914 caused Posix Port to fail to build on MacOS. This PR fixes
teh build failure.

This PR also adds a Matrix configuration to the GitHub kernel-demo
workflow to build the Posix Demos on MacOS.
---------

Co-authored-by: chinglee-iot <61685396+chinglee-iot@users.noreply.github.com>
Co-authored-by: Gaurav-Aggarwal-AWS <33462878+aggarg@users.noreply.github.com>

.github/workflows/kernel-demos.yml

@@ -65,7 +65,13 @@ jobs:
 
   POSIX-GCC:
     name: Native GCC
-    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - macos-latest
+          - ubuntu-latest
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout the FreeRTOS/FreeRTOS Repository
         uses: actions/checkout@v3
@@ -83,6 +89,7 @@ jobs:
 
       - name: Install GCC
         shell: bash
+        if: matrix.os == 'ubuntu-latest'
         run: |
           sudo apt-get -y update
           sudo apt-get -y install build-essential

portable/ThirdParty/GCC/Posix/port.c

@@ -57,6 +57,7 @@
 
 #include <errno.h>
 #include <pthread.h>
+#include <limits.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -281,10 +282,15 @@ BaseType_t xPortStartScheduler( void )
      */
     xSchedulerEnd = pdFALSE;
 
-    /* Reset the pthread_once_t structure. This is required if the port
-     * starts the scheduler again. */
-    hSigSetupThread = PTHREAD_ONCE_INIT;
-
+    /* Reset pthread_once_t, needed to restart the scheduler again.
+     * memset the internal struct members for MacOS/Linux Compatability */
+    #if __APPLE__
+        hSigSetupThread.__sig = _PTHREAD_ONCE_SIG_init;
+        memset( ( void * ) &hSigSetupThread.__opaque, 0, sizeof(hSigSetupThread.__opaque));
+    #else /* Linux PTHREAD library*/
+        hSigSetupThread = PTHREAD_ONCE_INIT;
+    #endif /* __APPLE__*/
+    
     /* Restore original signal mask. */
     ( void ) pthread_sigmask( SIG_SETMASK, &xSchedulerOriginalSignalMask, NULL );