BaseTools GCC: move PECOFF_HEADER_SIZE definition before LD script

BaseTools GCC: move PECOFF_HEADER_SIZE definition before LD script

Older versions of binutils need all symbols to be defined when consuming
the linker script passed via the command line. So move the definition
'--defsym=PECOFF_HEADER_SIZE=...' before the '--script=...' command line
argument.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18747 6f19259b-4bc3-4df7-8a09-765794883524