Do not hard-code -g and -O2 in CFLAGS

Let the user decide on the optimization level and debugging info.

Change-Id: I4b0b523b7dac4d67413bda37b546964262e5ea0d
diff --git a/lib/Makefile.am b/lib/Makefile.am
index 5bd9443..9dcd13b 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -2,7 +2,7 @@
 
 noinst_HEADERS = gnugetopt.h ippool.h lookup.h syserr.h tun.h in46_addr.h netdev.h gtp-kernel.h netns.h util.h icmpv6.h checksum.h
 
-AM_CFLAGS = -O2 -fno-builtin -Wall -DSBINDIR='"$(sbindir)"' -ggdb $(LIBOSMOCORE_CFLAGS)
+AM_CFLAGS = -fno-builtin -Wall -DSBINDIR='"$(sbindir)"' $(LIBOSMOCORE_CFLAGS)
 
 libmisc_a_SOURCES = getopt1.c getopt.c ippool.c lookup.c tun.c debug.c in46_addr.c netdev.c netns.c util.c icmpv6.c checksum.c