build: obey CFLAGS from libosmocore

When libosmocore is installed with an non standard prefix, the build
fails with non-found headers. e.g.

../liblogging/logging.h:3:10: fatal error: osmocom/core/logging.h: No such file or directory

src/liblogging/Makefile.am

@@ -1,4 +1,11 @@
-AM_CPPFLAGS = -Wall -Wextra -g $(all_includes)
+AM_CPPFLAGS = \
+        $(all_includes) \
+        $(NULL)
+
+AM_CFLAGS = \
+        -Wall -Wextra \
+        $(LIBOSMOCORE_CFLAGS) \
+        $(NULL)
 
 noinst_LIBRARIES = liblogging.a
 

src/liboptions/Makefile.am

@@ -1,4 +1,11 @@
-AM_CPPFLAGS = -Wall -Wextra -g $(all_includes)
+AM_CPPFLAGS = \
+        $(all_includes) \
+        $(NULL)
+
+AM_CFLAGS = \
+        -Wall -Wextra \
+        $(LIBOSMOCORE_CFLAGS) \
+        $(NULL)
 
 noinst_LIBRARIES = liboptions.a
 

src/sip/Makefile.am

@@ -1,4 +1,12 @@
-AM_CPPFLAGS = -Wall -Wextra -g $(all_includes) $(SOFIA_CFLAGS)
+AM_CPPFLAGS = \
+        $(all_includes) \
+        $(NULL)
+
+AM_CFLAGS = \
+        -Wall -Wextra \
+        $(SOFIA_CFLAGS) \
+        $(LIBOSMOCORE_CFLAGS) \
+        $(NULL)
 
 bin_PROGRAMS = \
 	osmo-cc-sip-endpoint