configure: use LIB_EXT rather than hardcoded .so

Some platforms different library extension - dll, dylib, a.
Honor that when we are creating the required links.

Rename LIB_EXTENSION to LIB_EXT while we're here.

With libglapi linking aside, building classic drivers on
non-linux platforms should be possible now.

v2: Resolve conflicts.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Jon TURNEY <jon.turney@dronecode.org.uk>
diff --git a/install-lib-links.mk b/install-lib-links.mk
index 9dd4c30..2707eb8 100644
--- a/install-lib-links.mk
+++ b/install-lib-links.mk
@@ -5,7 +5,7 @@
 
 .libs/install-mesa-links : $(lib_LTLIBRARIES)
 	$(AM_V_GEN)$(MKDIR_P) $(top_builddir)/$(LIB_DIR);	\
-	for f in $(lib_LTLIBRARIES:%.la=.libs/%.so*); do	\
+	for f in $(lib_LTLIBRARIES:%.la=.libs/%.$(LIB_EXT)*); do \
 		if test -h .libs/$$f; then			\
 			cp -d $$f $(top_builddir)/$(LIB_DIR);	\
 		else						\