Fix strict aliasing violation from conditional typedef of wchar_t by building entire project as C++ for Unix (#6801)

Enable building CoreCLR as C++ project on Unix

This series of patches fixes the strict aliasing violation from
the conditional typedef of wchar_t in src/pal/inc/pal_char16.h:40

* rename c files to cpp
* modify all cmake files to change .c files to .cpp
* apply c++ linkage to templates

1 files changed, 82 insertions, 0 deletions

diff --git a/src/pal/tests/palsuite/c_runtime/fopen/test4/test4.cpp b/src/pal/tests/palsuite/c_runtime/fopen/test4/test4.cpp
new file mode 100644
index 0000000000..04683d52c5
--- /dev/null
+++ b/src/pal/tests/palsuite/c_runtime/fopen/test4/test4.cpp
@@ -0,0 +1,82 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+/*=====================================================================
+**
+** Source:  test4.c
+**
+** Purpose: Tests the PAL implementation of the fopen function. 
+**          Test to ensure that you can't write to a 'r' mode file.
+**          And that you can read from a 'r' mode file.
+**
+** Depends:
+**      fprintf
+**      fclose
+**      fgets
+**  
+
+**
+**===================================================================*/
+                                                                         
+#include <palsuite.h>
+
+int __cdecl main(int argc, char **argv)
+{
+  
+    FILE *fp;
+    char buffer[128];
+  
+    if (PAL_Initialize(argc, argv))
+    {
+        return FAIL;
+    }
+
+  
+    /* Open a file with 'w' mode */
+    if( (fp = fopen( "testfile", "w" )) == NULL )
+    {
+        Fail( "ERROR: The file failed to open with 'w' mode.\n" );
+    }  
+  
+    /* Write some text to the file */
+    if(fprintf(fp,"%s","some text") <= 0) 
+    {
+        Fail("ERROR: Attempted to WRITE to a file opened with 'w' mode "
+               "but fprintf failed.  Either fopen or fprintf have problems.");
+    }
+
+    if(fclose(fp))
+    {
+        Fail("ERROR: Attempted to close a file, but fclose failed. "
+               "This test depends upon it.");
+    }
+
+    /* Open a file with 'r' mode */
+    if( (fp = fopen( "testfile", "r" )) == NULL )
+    {
+        Fail( "ERROR: The file failed to open with 'r' mode.\n" );
+    } 
+  
+    /* Attempt to read from the 'r' only file, should pass */
+    if(fgets(buffer,10,fp) == NULL)
+    {
+        Fail("ERROR: Tried to READ from a file with 'r' mode set. "
+               "This should succeed, but fgets returned NULL.  Either fgets "
+               "or fopen is broken.");
+    }
+
+    /* Write some text to the file */
+    if(fprintf(fp,"%s","some text") > 0) 
+    {
+        Fail("ERROR: Attempted to WRITE to a file opened with 'r' mode "
+               "but fprintf succeeded  It should have failed.  "
+               "Either fopen or fprintf have problems.");
+    }
+
+
+    PAL_Terminate();
+    return PASS;
+}
+   
+