Remove the include of opt_global.h. It's included globally by a command
line switch. Other files which may make the same mistake (according to
fxr.watson.org) but aren't fixed in this commit (people with more clue
about those files should fix this):

• i386/xbox/xbox.c
• arm/arm/elf_trampoline.c
• arm/arm/mem.c

Noticed by: cognet