Fix issue 12965 - DMD sets ELFOSABI to ELFOSABI_LINUX on all systems

[jasonbking]

This will properly set the ELF OSABI field based on the target (for ELF targets).

https://issues.dlang.org/show_bug.cgi?id=12965

[dnadlinger]

Added bugzilla link to the original message.

[WalterBright]

Please align comments.

[jasonbking]

Added the requested tweaks.

[quickfur]

This pull broke dmd build on my LInux/64-bit machine:

backend/elfobj.c:14:0: error: unterminated #if
 #if SCPP || MARS
 ^
posix.mak:356: recipe for target 'elfobj.o' failed
make[1]: *** [elfobj.o] Error 1
make[1]: Leaving directory '/mnt/1/usr/src/d/dmd/src'
posix.mak:8: recipe for target 'all' failed
make: *** [all] Error 2

[quickfur]

Looks like it's missing an #endif at the end of the ELFOSABI block. How did this escape the autotester?!

[quickfur]

Fix: pull #3691

[jasonbking]

Eek! I had fixed this locally and thought I had pushed this out along with the other requested changes, but apparently did not. Sorry :(

[quickfur]

No problem, I already fixed it and the fix just got merged. I'm just surprised it got past the autotester somehow.

[yebblies]

No problem, I already fixed it and the fix just got merged. I'm just surprised it got past the autotester somehow.

It didn't, Walter just decided to merge it manually instead of using the autotester's auto-merge.

[quickfur]

Ah, figures.