Use AC_SEARCH_LIBS() for math functions.

Use it to check whether we need -lm for various math functions -
including floorl().  Let it handle adding -lm, rather than having that
in the various _LDADD macros.

Change-Id: Ic5d24ec35e060306351f4981c92e26879e597d81
Reviewed-on: https://code.wireshark.org/review/5908
Reviewed-by: Guy Harris <guy@alum.mit.edu>

Makefile.am

@@ -414,8 +414,7 @@ wireshark_common_ldadd = \
 	@LIBGCRYPT_LIBS@		\
 	@LIBGNUTLS_LIBS@		\
 	@LIBSMI_LDFLAGS@		\
-	@GLIB_LIBS@			\
-	-lm
+	@GLIB_LIBS@
 
 if HAVE_Qt
 wireshark_SOURCES = $(WIRESHARK_COMMON_SRC)
@@ -487,8 +486,8 @@ tshark_LDADD = \
 	@COREFOUNDATION_FRAMEWORKS@	\
 	@LIBGCRYPT_LIBS@		\
 	@LIBGNUTLS_LIBS@		\
-	@LIBSMI_LDFLAGS@		\
-	-lm
+	@LIBSMI_LDFLAGS@
+
 tshark_CFLAGS = $(AM_CLEAN_CFLAGS)
 
 if ENABLE_STATIC
@@ -514,8 +513,8 @@ tfshark_LDADD = \
 	@SYSTEMCONFIGURATION_FRAMEWORKS@	\
 	@COREFOUNDATION_FRAMEWORKS@	\
 	@LIBGNUTLS_LIBS@		\
-	@LIBSMI_LDFLAGS@		\
-	-lm
+	@LIBSMI_LDFLAGS@
+
 tfshark_CFLAGS = $(AM_CLEAN_CFLAGS)
 
 if ENABLE_STATIC
@@ -544,15 +543,15 @@ rawshark_LDADD = \
 	@COREFOUNDATION_FRAMEWORKS@	\
 	@LIBGCRYPT_LIBS@		\
 	@LIBGNUTLS_LIBS@		\
-	@LIBSMI_LDFLAGS@		\
-	-lm
+	@LIBSMI_LDFLAGS@
+
 rawshark_CFLAGS = $(AM_CLEAN_CFLAGS)
 
 # Libraries with which to link text2pcap.
 text2pcap_LDADD = \
 	wsutil/libwsutil.la		\
-	@GLIB_LIBS@			\
-	-lm
+	@GLIB_LIBS@
+
 # Don't turn on -Werror for text2pcap: its source includes text2pcap-scanner.c
 # which is generated (and therefore not always clean).
 # We could generate text2pcap.o as a library with -Werror but for now it
@@ -604,8 +603,8 @@ randpkt_LDADD = \
 	@SOCKET_LIBS@			\
 	@NSL_LIBS@			\
 	@C_ARES_LIBS@			\
-	@ADNS_LIBS@			\
-	-lm
+	@ADNS_LIBS@
+
 randpkt_CFLAGS = $(AM_CLEAN_CFLAGS)
 
 # Libraries and plugin flags with which to link dftest.
@@ -625,8 +624,8 @@ dftest_LDADD = \
 	@KRB5_LIBS@			\
 	@LIBGCRYPT_LIBS@		\
 	@LIBGNUTLS_LIBS@		\
-	@LIBSMI_LDFLAGS@		\
-	-lm
+	@LIBSMI_LDFLAGS@
+
 dftest_CFLAGS = $(AM_CLEAN_CFLAGS)
 
 echld_test_LDADD = \
@@ -638,8 +637,7 @@ echld_test_LDADD = \
 	@SOCKET_LIBS@			\
 	@NSL_LIBS@			\
 	@C_ARES_LIBS@			\
-	@ADNS_LIBS@			\
-	-lm
+	@ADNS_LIBS@
 
 echld_test_DEPENDENCIES = \
 	echld/libechld.la \

configure.ac

@@ -506,6 +506,23 @@ AC_SUBST(OSX_MIN_VERSION)
 #
 AC_SYS_LARGEFILE
 
+#
+# Look for math functions; use libm if necessary.
+#
+AC_SEARCH_LIBS(floor, m)
+AC_SEARCH_LIBS(ceil, m)
+AC_SEARCH_LIBS(exp, m)
+AC_SEARCH_LIBS(log, m)
+AC_SEARCH_LIBS(log10, m)
+AC_SEARCH_LIBS(floorl, m,
+  [
+    FLOORL_LO=""
+    AC_DEFINE(HAVE_FLOORL, 1, [Define if you have the floorl function.])
+  ],
+  FLOORL_LO="floorl.lo")
+AC_SUBST(FLOORL_LO)
+
+
 #
 # GUI toolkit options
 #
@@ -2648,14 +2665,6 @@ AC_C_BIGENDIAN
 # XXX - do we need this?
 AC_PROG_GCC_TRADITIONAL
 
-AC_CHECK_FUNC(floorl,
-  [
-    FLOORL_LO=""
-    AC_DEFINE(HAVE_FLOORL, 1, [Define if you have the floorl function.])
-  ],
-  FLOORL_LO="floorl.lo")
-AC_SUBST(FLOORL_LO)
-
 AC_CHECK_FUNC(getopt,
   [
     GETOPT_LO=""