Pullup ticket #4315 - requested by obache
emulators/dosbox: build fix

Revisions pulled up:
- emulators/dosbox/Makefile                                     1.38

---
   Module Name:	pkgsrc
   Committed By:	obache
   Date:		Wed Feb  5 08:40:11 UTC 2014

   Modified Files:
   	pkgsrc/emulators/dosbox: Makefile

   Log Message:
   Restrict CPPFLAGS=-fPIC to clang only, as changed reason.

   At least, It break build on NetBSD-i386 with buitin gcc, PR pkg/48538.
   No build failure on NetBSD-amd64 with builtin gcc.
Pullup ticket #4315.