Fix mach-o static builds by forcing all code that's linked into a shared lib to build with -fPIC.

Bug #194662 r=ccarlen

layout/inspector/src/Makefile.in

@@ -69,5 +69,7 @@ DIRS		+= win
 endif
 
 FORCE_STATIC_LIB = 1
+# This library is used by other shared libs in a static build
+FORCE_USE_PIC = 1
 
 include $(topsrcdir)/config/rules.mk