Blackberry mkspecs: Refine compiler options

Blackberry mkspecs: Refine compiler options

stack-protector-strong gives performance benefits over
stack-protector-all and is still checking more than -stack-protector,
so seems to be a good middle way and we want to use it when it is
there.

The -shared option for the compiler (not the linker) prevents a
RIM internal version of qcc from forcing -fPIE, and should not harm
in general when set.

In addition, add a method "compilerSupportsFlag" for Windows as is
present in the Unix configure script.

Change-Id: Iba300e9cb82f34043e7b36f8e45287a1aed2a1a5
Original-patch-by: Greg Bentz
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>