BaseTools/Source/C: Remove duplicate -fshort-wchar

`-fshort-wchar -flto -DUSING_LTO` was added via CPPFLAGS to all relevant
uses of gcc and g++ in commit 2f61ab9.

However CFLAGS, as defined in the lines above that change, is never
consumed without CPPFLAGS, therefore `-fshort-wchar` can be removed from
CFLAGS to avoid it appearing twice in every call to gcc which uses CFLAGS.

Note that the affected files within BaseTools/Source/C (those that
include the changed file, and all those that those include) are:

```
Makefiles/app.makefile
Makefiles/lib.makefile
GNUmakefile
VfrCompile/GNUmakefile
Makefiles/footer.makefile
Makefiles/header.makefile
```

Note also that in VfrCompile/GNUmakefile g++ is affected by CPPFLAGS,
but not CXXFLAGS.

Signed-off-by: Mike Beaton <mjsbeaton@gmail.com>

Author: mikebeaton

BaseTools/Source/C/Makefiles/header.makefile

@@ -97,16 +97,16 @@ BUILD_OPTFLAGS = -O2 $(EXTRA_OPTFLAGS)
 
 ifeq ($(DARWIN),Darwin)
 # assume clang or clang compatible flags on OS X
-CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror \
+CFLAGS = -MD -fno-strict-aliasing -Wall -Werror \
 -Wno-deprecated-declarations -Wno-self-assign -Wno-unused-result -nostdlib -g
 else
 ifneq ($(CLANG),)
-CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -fwrapv \
+CFLAGS = -MD -fno-strict-aliasing -fwrapv \
 -fno-delete-null-pointer-checks -Wall -Werror \
 -Wno-deprecated-declarations -Wno-self-assign \
 -Wno-unused-result -nostdlib -g
 else
-CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -fwrapv \
+CFLAGS = -MD -fno-strict-aliasing -fwrapv \
 -fno-delete-null-pointer-checks -Wall -Werror \
 -Wno-deprecated-declarations -Wno-stringop-truncation -Wno-restrict \
 -Wno-unused-result -nostdlib -g