add: linking libm on demand

Author: robert-burger

configure.ac

@@ -176,6 +176,9 @@ AC_FUNC_MALLOC
 AC_FUNC_REALLOC
 AC_CHECK_FUNCS([clock_gettime memset socket strdup strerror strndup]) #pthread_setaffinity_np])
 
+AC_CHECK_LIB(m, sqrt, MATH_LIBS="-lm")
+AC_SUBST(MATH_LIBS)
+
 AC_CONFIG_FILES([Makefile src/Makefile tools/ethercatdiag/Makefile tools/eepromtool/Makefile tools/example_with_dc/Makefile tools/foe_tool/Makefile libethercat.pc])
 AC_OUTPUT
 

tools/example_with_dc/Makefile.am

@@ -1,7 +1,7 @@
 ACLOCAL_AMFLAGS = -I m4
 
 LDADD = $(top_builddir)/src/.libs/libethercat.la
-LIBS  = @LIBOSAL_LIBS@ -lm
+LIBS  = @LIBOSAL_LIBS@ @MATH_LIBS@
 
 bin_PROGRAMS = example_with_dc
 example_with_dc_SOURCES = example_with_dc.c