BaseTools: Add GCC flags to Basetool build.

BaseTools: Add GCC flags to Basetool build.

BZ:https://bugzilla.tianocore.org/show_bug.cgi?id=1764

Some compiler flags restrict the compiler from making
arbitrary decisions while handling undefined C/C++ behaviors.
Therefore they can be used to fix some issues caused by undefined behavior.

For example, for GCC, the following flags are available:
-fno-delete-null-pointer-checks tells
the compiler NOT to assume that null pointer deference does not exist.
-fwrapv tells the compiler that signed overflow always wraps.

This patch is going to add these 2 build options to
BaseTool GCC build option.

Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>