build: remove unused all_includes and use AM_CPPFLAGS

Preprocessor flags are best placed in AM_CPPFLAGS. Remove use of the
unused all_includes variable, which is never set.
diff --git a/Makefile.am b/Makefile.am
index f2899cc..faf7a83 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,6 +1,5 @@
 ACLOCAL_AMFLAGS = -I m4
 
-AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include
 SUBDIRS = include src src/vty src/codec src/gsm src/gb src/ctrl tests utils
 
 pkgconfigdir = $(libdir)/pkgconfig
diff --git a/src/Makefile.am b/src/Makefile.am
index f2b1b83..65494a5 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -2,7 +2,8 @@
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
 LIBVERSION=5:0:0
 
-AM_CFLAGS = -Wall $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CFLAGS = -Wall
 
 lib_LTLIBRARIES = libosmocore.la
 
diff --git a/src/codec/Makefile.am b/src/codec/Makefile.am
index f4dec62..b4834e5 100644
--- a/src/codec/Makefile.am
+++ b/src/codec/Makefile.am
@@ -2,7 +2,8 @@
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
 LIBVERSION=0:0:0
 
-AM_CFLAGS = -Wall $(all_includes) -I$(top_srcdir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include
+AM_CFLAGS = -Wall
 
 lib_LTLIBRARIES = libosmocodec.la
 
diff --git a/src/gb/Makefile.am b/src/gb/Makefile.am
index 8a96628..70caa1f 100644
--- a/src/gb/Makefile.am
+++ b/src/gb/Makefile.am
@@ -2,7 +2,8 @@
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
 LIBVERSION=3:1:0
 
-AM_CFLAGS = -Wall ${GCC_FVISIBILITY_HIDDEN} -fno-strict-aliasing $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CFLAGS = -Wall ${GCC_FVISIBILITY_HIDDEN} -fno-strict-aliasing
 
 # FIXME: this should eventually go into a milenage/Makefile.am
 noinst_HEADERS = common_vty.h
diff --git a/src/gsm/Makefile.am b/src/gsm/Makefile.am
index 9c7df5a..828aa50 100644
--- a/src/gsm/Makefile.am
+++ b/src/gsm/Makefile.am
@@ -2,7 +2,8 @@
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
 LIBVERSION=6:0:1
 
-AM_CFLAGS = -Wall ${GCC_FVISIBILITY_HIDDEN} $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CFLAGS = -Wall ${GCC_FVISIBILITY_HIDDEN}
 
 # FIXME: this should eventually go into a milenage/Makefile.am
 noinst_HEADERS = milenage/aes.h milenage/aes_i.h milenage/aes_wrap.h \
diff --git a/src/vty/Makefile.am b/src/vty/Makefile.am
index 2e234c8..d4be3f0 100644
--- a/src/vty/Makefile.am
+++ b/src/vty/Makefile.am
@@ -2,7 +2,8 @@
 # Please read Chapter 6 "Library interface versions" of the libtool documentation before making any modification
 LIBVERSION=0:1:0
 
-AM_CFLAGS = -Wall $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
+AM_CFLAGS = -Wall
 
 if ENABLE_VTY
 lib_LTLIBRARIES = libosmovty.la
diff --git a/tests/Makefile.am b/tests/Makefile.am
index ea4bf9c..8779c4f 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1,4 +1,5 @@
-AM_CFLAGS = -Wall $(all_includes) -I$(top_srcdir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include
+AM_CFLAGS = -Wall
 
 check_PROGRAMS = timer/timer_test sms/sms_test ussd/ussd_test		\
                  smscb/smscb_test bits/bitrev_test a5/a5_test		\
diff --git a/utils/Makefile.am b/utils/Makefile.am
index 6a3cd12..51c884a 100644
--- a/utils/Makefile.am
+++ b/utils/Makefile.am
@@ -1,5 +1,6 @@
 if ENABLE_UTILITIES
-AM_CFLAGS = -Wall $(all_includes) -I$(top_srcdir)/include
+AM_CPPFLAGS = -I$(top_srcdir)/include
+AM_CFLAGS = -Wall
 
 bin_PROGRAMS = osmo-arfcn osmo-auc-gen