[gegl] build: Use $MATH_LIB instead of -lm for portability and consistency

[Debarshi Ray <debarshir src gnome org>]

commit 3c6e9bade718c2a1bfcc2460878a841ff79486aa
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Jan 26 12:43:42 2018 +0100

    build: Use $MATH_LIB instead of -lm for portability and consistency

 gegl/Makefile.am |    2 +-
 perf/Makefile.am |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gegl/Makefile.am b/gegl/Makefile.am
index c139754..e0e1972 100644
--- a/gegl/Makefile.am
+++ b/gegl/Makefile.am
@@ -41,7 +41,7 @@ AM_LDFLAGS = \
        $(no_undefined) -export-dynamic -version-info $(GEGL_LIBRARY_VERSION)
 
 LIBS = \
-       $(DEP_LIBS) $(BABL_LIBS) -lm
+       $(DEP_LIBS) $(BABL_LIBS) $(MATH_LIB)
 
 GEGL_publicdir = $(includedir)/gegl-$(GEGL_API_VERSION)
 
diff --git a/perf/Makefile.am b/perf/Makefile.am
index a45ef8f..e0cf505 100644
--- a/perf/Makefile.am
+++ b/perf/Makefile.am
@@ -30,7 +30,7 @@ AM_CPPFLAGS = \
 
 common_ldadd = $(top_builddir)/gegl/libgegl-@GEGL_API_VERSION@.la
 
-LDADD = $(common_ldadd) $(DEP_LIBS) $(BABL_LIBS) -lm
+LDADD = $(common_ldadd) $(DEP_LIBS) $(BABL_LIBS) $(MATH_LIB)
 
 perf-report: check