Unusable header fix-ups

IOhannes m zmoelnig reported (via https://bugs.debian.org/761191) that a few
headers are missing the leading / in their boilerplate, which renders them
unusable. The attached patch (against master) fixes this; it applies to
stable too.

Patch by Stephen Kitt -- skitt at debian.org
Fix missing source

Attached patch fix listed source for mingwex{32,64} introduced in
commit [3e3f329]

Patch by Alexey Pavlov (alexpux at gmail dot com)
Regenerate Makefile.in
Don't build directx related import libraries on ARM
stdio: Implement assembler forwards for ARM
misc: Implement mingw_getsp for ARM