[ELF] - Stop mixing order of -defsym/-script commands.

Previously we always handled -defsym after other commands in command line.
That made impossible to overload values set by -defsym from linker script:

 test.script:            
  foo = 0x22;
-defsym=foo=0x11 -script t.script
would always set foo to 0x11.

That is inconstent with common logic which allows to override command line
options. it is inconsistent with bfd behavior and seems breaks assumption that
-defsym is the same as linker script assignment, as -defsyms always handled out of
command line order.

Patch fixes the handling order.

Differential revision: https://reviews.llvm.org/D42054

llvm-svn: 322625