configure: On Solaris, libpng requires libm.

configure

@@ -16044,7 +16044,7 @@ if test "${ac_cv_lib_soname_png+set}" = set; then
   echo $ECHO_N "(cached) $ECHO_C" >&6
 else
   ac_check_soname_save_LIBS=$LIBS
-LIBS="-lpng  $LIBS"
+LIBS="-lpng -lm $LIBS"
   cat >conftest.$ac_ext <<_ACEOF
 /* confdefs.h.  */
 _ACEOF

configure.ac

@@ -1201,7 +1201,7 @@ WINE_WARNING_WITH(jpeg,[test "x$ac_cv_lib_soname_jpeg" = "x"],
 dnl **** Check for libpng ****
 if test "$ac_cv_header_png_h" = "yes"
 then
-    WINE_CHECK_SONAME(png,png_create_read_struct,,,,[[libpng[[0-9]]*]])
+    WINE_CHECK_SONAME(png,png_create_read_struct,,,-lm,[[libpng[[0-9]]*]])
 fi
 WINE_WARNING_WITH(png,[test "x$ac_cv_lib_soname_png" = "x"],
                  [libpng development files not found, PNG won't be supported.])