UnitTestFrameworkPkg: Add code coverage support for GCC

In order to collect code coverage after running executable
file, generate *.gcda and *.gcno file that require by lcov tool
to generate code coverage report.

Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Reviewed-by: Michael Kubacki <mikuback@linux.microsoft.com>
Signed-off-by: Gua Guo <gua.guo@intel.com>

UnitTestFrameworkPkg/UnitTestFrameworkPkgHost.dsc.inc

@@ -27,7 +27,8 @@
   GCC:*_*_*_CC_FLAGS   = -D UNIT_TESTING_DEBUG=1
   XCODE:*_*_*_CC_FLAGS = -D UNIT_TESTING_DEBUG=1
 !endif
-
+  GCC:*_GCC5_*_CC_FLAGS = --coverage
+  GCC:*_GCC5_*_DLINK_FLAGS = --coverage
 [BuildOptions.common.EDKII.HOST_APPLICATION]
   #
   # MSFT