Implemented a gcm plugin providing GCM mode based on CBC crypters

src/libstrongswan/plugins/gcm/Makefile.am

@@ -0,0 +1,16 @@
+
+INCLUDES = -I$(top_srcdir)/src/libstrongswan
+
+AM_CFLAGS = -rdynamic
+
+if MONOLITHIC
+noinst_LTLIBRARIES = libstrongswan-gcm.la
+else
+plugin_LTLIBRARIES = libstrongswan-gcm.la
+endif
+
+libstrongswan_gcm_la_SOURCES = \
+	gcm_plugin.h gcm_plugin.c \
+	gcm_aead.h gcm_aead.c
+
+libstrongswan_gcm_la_LDFLAGS = -module -avoid-version