Don't try to build an empty library (on platforms where this is no shell service impl). Bug 252207.

browser/components/shell/src/Makefile.in

@@ -27,7 +27,6 @@ VPATH   = @srcdir@
 include $(DEPTH)/config/autoconf.mk
 
 MODULE = shellservice
-LIBRARY_NAME = shellservice_s
 
 REQUIRES	= \
 		  xpcom \
@@ -60,6 +59,10 @@ endif
 endif
 endif
 
+ifdef CPPSRCS
+LIBRARY_NAME = shellservice_s
+endif
+
 FORCE_STATIC_LIB = 1
 
 include $(topsrcdir)/config/rules.mk