Check GNU linker instead of gcc compiler for exported symbols control.

Also enable unix OSs other than linux, kfreebsd and hurd.  macos isn't
affected because it doesn't use GNU ld.

NEWS

@@ -1,5 +1,7 @@
 Unreleased
   * Switch to GCC's visibility for hiding more implementation details
+  * Check GNU ld instead of gcc for exported symbols control logic in
+    configure.ac
 
 Version 0.2.1 (2021-01-23)
   * Fix incorrect passing of -version-info to libtool, causing a

configure.ac

@@ -260,14 +260,13 @@ AS_IF([test "x$enable_werror" = "xyes"], [
 AX_APPEND_COMPILE_FLAGS([-W -Wstrict-prototypes -Wmissing-prototypes -Wall -Waggregate-return -Wcast-align -Wcast-qual -Wnested-externs -Wshadow -Wpointer-arith], [CFLAGS])
 
 dnl ====================================================================================
-dnl  GCC stuff.
+dnl  Exported symbols control.
 
-AS_IF([test "x$ax_cv_c_compiler_vendor" = "xgnu"], [
-		# OS specific tweaks.
+AS_IF([test "x$lt_cv_prog_gnu_ld" = "xyes"], [
 		AS_CASE([${host_os}],
 			[mingw*|cygwin*], [
 				SHLIB_VERSION_ARG="-export-symbols \$(top_srcdir)/Win32/libsamplerate-0.def"],
-			[linux*|kfreebsd*-gnu*|gnu*], [
+			[*], [
 				SHLIB_VERSION_ARG="-Wl,--version-script=\$(top_builddir)/src/Version_script"
 			])
 	])