CryptoPkg SysCall Lib: Fix warning with GCC in CrtWrapper.c

CryptoPkg SysCall Lib: Fix warning with GCC in CrtWrapper.c

Exit is declared to be 'noreturn' function, but GCC sees
that the empty function will return.  Therefore, GCC flags
a warning.

To work-around this, we use a function pointer, along with
a cast to force the code to think that a 'noreturn' function
is being called.

Signed-off-by: jljusten
Reviewed-by: qlong
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11609 6f19259b-4bc3-4df7-8a09-765794883524