Taken from https://bug1339931.bmoattachments.org/attachment.cgi?id=8837770.

Add major version to pkg-config filename.
Author: Rico Tzschichholz <ricotz@ubuntu.com>
Forwarded: no
Last-Update: 2015-05-04

Index: b/js/src/Makefile.in
===================================================================
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -214,10 +214,10 @@
 $(JS_CONFIG_NAME): js-config
    cp $^ $@
 
-$(LIBRARY_NAME).pc: js.pc
+$(JS_LIBRARY_NAME).pc: js.pc
 	cp $^ $@
 
-install:: $(LIBRARY_NAME).pc
+install:: $(JS_LIBRARY_NAME).pc
 	$(SYSINSTALL) $^ $(DESTDIR)$(libdir)/pkgconfig
 
 install:: js-config.h
