Use build_cc to compile the programs to run on build host
helps with cross compiling

Upstream-Status: Inappropriate [Cross-compiled OE specific]

diff --git a/src/common/mathvariants/Makefile.am b/src/common/mathvariants/Makefile.am
index 636ccf0..ed9921d 100644
--- a/src/common/mathvariants/Makefile.am
+++ b/src/common/mathvariants/Makefile.am
@@ -52,7 +52,7 @@ XSLTPROC = xsltproc
 %.cc : %_gen.cc $(srcdir)/variant.top $(srcdir)/variant.bot
 	cat $(srcdir)/variant.top >$@
 	$(XSLTPROC) --novalid --param temp "false()" $(srcdir)/extract.xsl $(<:%_gen.cc=$(srcdir)/xml/%.xml) >>$@
-	$(CXX) -o $(@:%.cc=%) -I$(top_builddir)/auto $<
+	$(BUILD_CXX) -o $(@:%.cc=%) -I$(top_builddir)/auto $<
 	echo "Char32 " >>$@
 	basename map_variant_$@ .cc | tr "-" "_" >>$@
 	echo "(Char32 ch)" >>$@