Use bash explicitly when calling build_tools/mkpkgconfig from the Makefile.

Since we use bashisms in build_tools/mkpkgconfig, we should call on bash
explicitly when running from the Makefile, otherwise we get errors during a
'make install.'

(closes issue #15209)
Reported by: seandarcy


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@197260 65c4cc65-6c06-0410-ace0-fbb531ad65f3

Makefile

@@ -472,7 +472,7 @@ distclean: $(SUBDIRS_DIST_CLEAN) _clean
 	rm -f build_tools/menuselect-deps
 
 datafiles: _all
-	if [ x`$(ID) -un` = xroot ]; then CFLAGS="$(ASTCFLAGS)" sh build_tools/mkpkgconfig $(DESTDIR)/usr/lib/pkgconfig; fi
+	if [ x`$(ID) -un` = xroot ]; then CFLAGS="$(ASTCFLAGS)" bash build_tools/mkpkgconfig $(DESTDIR)/usr/lib/pkgconfig; fi
 # Should static HTTP be installed during make samples or even with its own target ala
 # webvoicemail?  There are portions here that *could* be customized but might also be
 # improved a lot.  I'll put it here for now.