Fix PIC CFLAGS

Fix PIC CFLAGS

Commit 8eca6a1153eb7768c2f29ea2d48f01f6988cbfe3 just used -fPIC to
generate position-independant code. However, the flag to turn on PIC
varies depending on the compiler, and is not always -fPIC. Just use
SHD_CCRULE instead, which will get us the correct PIC flags.

Change-Id: I61d698587cc3959b35ec27abe3c3b19adab5d8f1
Reviewed-on: http://gerrit.openafs.org/3962
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>