MdePkg: Update code to be more C11 compliant by using __func__

__FUNCTION__ is a pre-standard extension that gcc and Visual C++ among
others support, while __func__ was standardized in C99.

Since it's more standard, replace __FUNCTION__ with __func__ throughout
MdePkg.

Visual Studio versions before VS 2015 don't support __func__ and so
will fail to compile. A workaround is to define __func__ as
__FUNCTION__ :

 #define __func__ __FUNCTION__

Signed-off-by: Rebecca Cran <rebecca@quicinc.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>

MdePkg/Library/BaseLib/SafeString.c

@@ -17,7 +17,7 @@
     if (!(Expression)) { \
       DEBUG ((DEBUG_VERBOSE, \
         "%a(%d) %a: SAFE_STRING_CONSTRAINT_CHECK(%a) failed.  Return %r\n", \
-        __FILE__, DEBUG_LINE_NUMBER, __FUNCTION__, DEBUG_EXPRESSION_STRING (Expression), Status)); \
+        __FILE__, DEBUG_LINE_NUMBER, __func__, DEBUG_EXPRESSION_STRING (Expression), Status)); \
       return Status; \
     } \
   } while (FALSE)