configure.ac: Resolve libnatpmp conftest issue.

Do not unnecessarily clutter CPPFLAGS; the variable is honored by
Autoconf while running its conftests and can cause issues such as
symbol clashes between the libnatpmp and webrtc-audio-processing
library observed below:

configure:20851: checking for initnatpmp in -lnatpmp
configure:20873: g++ -std=gnu++17 -o conftest  -DNDEBUG=1 -O3 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -DPJ_AUTOCONF=1  -I/home/maxim/src/ring-project/daemon/contrib/x86_64-unknown-linux-gnu/include  -fvisibility=hidden -DDRING_BUILD  -Ddring_EXPORTS  -DASIO_STANDALONE -I/home/maxim/src/ring-project/daemon/contrib/x86_64-unknown-linux-gnu/include -I/gnu/store/zimpk6gqmjrwxc7fnam212kv3a6dwpzz-jsoncpp-1.9.2/include -DWEBRTC_AUDIO_PROCESSING_ONLY_BUILD -DWEBRTC_POSIX -I/home/maxim/src/ring-project/daemon/contrib/x86_64-unknown-linux-gnu/include/webrtc_audio_processing  -Wl,-Bsymbolic -ldl -L/home/maxim/src/ring-project/daemon/contrib/x86_64-unknown-linux-gnu/lib -L/gnu/store/zimpk6gqmjrwxc7fnam212kv3a6dwpzz-jsoncpp-1.9.2/lib -ljsoncpp -L/home/maxim/src/ring-project/daemon/contrib/x86_64-unknown-linux-gnu/lib -lwebrtc_audio_processing conftest.cpp -lnatpmp -lpthread  -lssl -lcrypto >&5
ld: /tmp/cc5prP4w.o: in function `main':
conftest.cpp:(.text.startup+0x0): multiple definition of `main'; /home/maxim/src/ring-project/daemon/contrib/x86_64-unknown-linux-gnu/lib/libwebrtc_audio_processing.a(libwebrtc_audio_processing_la-click_annotate.o):click_annotate.cc:(.text.startup+0x0): first defined here
collect2: error: ld returned 1 exit status
configure:20873: $? = 1

This was causing the link test of the libnatpmp library to fail,
which in turned caused the natpmp support to be disabled entirely.

* src/Makefile.am (libring_la_LDFLAGS): Add @WEBRTC_LIBS@.
(libring_la_CFLAGS): Add @WEBRTC_CFLAGS@.
* src/media/audio/Makefile.am (libaudio_la_CXXFLAGS)
[HAVE_WEBRTC_AP]: Add @WEBRTC_CFLAGS@.
* src/media/audio/echo-cancel/Makefile.am
(libecho_cancel_la_CXXFLAGS): Add @WEBRTC_CFLAGS@ and honor AM_CXXFLAGS.

GitLab: #487
Change-Id: I064d6a563318b34b2f3f516ca2aa8c2831205b09

configure.ac

@@ -555,9 +555,8 @@ AC_ARG_WITH([webrtcap],
 AS_IF([test "x$with_webrtc_ap" = "xyes"],
       [PKG_CHECK_MODULES(WEBRTC, [webrtc-audio-processing >= 0.3.1],
         [
-          AC_DEFINE([HAVE_WEBRTC_AP], 1, [Define if you have webrtc-audio-processing])
-          CPPFLAGS="${CPPFLAGS} ${WEBRTC_CFLAGS}"
-          LDFLAGS="${LDFLAGS} ${WEBRTC_LIBS}"
+          AC_DEFINE([HAVE_WEBRTC_AP], 1,
+                    [Define if you have webrtc-audio-processing])
         ],
         AC_MSG_WARN([Missing webrtc-audio-processing development files]))
       ])

src/Makefile.am

@@ -77,7 +77,8 @@ libring_la_LDFLAGS = \
 		@LIBSWRESAMPLE_LIBS@ \
 		@LIBSWSCALE_LIBS@ \
 		@LIBAVUTIL_LIBS@ \
-		@LIBS@
+		@LIBS@ \
+		@WEBRTC_LIBS@
 
 if ENABLE_PLUGIN
 libring_la_LDFLAGS+= \
@@ -109,7 +110,8 @@ libring_la_CFLAGS = \
 		@LIBAVDEVICE_CFLAGS@ \
 		@LIBAVFILTER_CFLAGS@ \
 		@LIBSWRESAMPLE_CFLAGS@ \
-		@LIBSWSCALE_CFLAGS@
+		@LIBSWSCALE_CFLAGS@ \
+		@WEBRTC_CFLAGS@
 
 libring_la_CXXFLAGS = @JSONCPP_CFLAGS@
 

src/media/audio/Makefile.am

@@ -61,6 +61,10 @@ libaudio_la_CXXFLAGS += @SPEEXDSP_CFLAGS@
 libaudio_la_LDFLAGS += @SPEEXDSP_LIBS@
 endif
 
+if HAVE_WEBRTC_AP
+libaudio_la_CXXFLAGS += @WEBRTC_CFLAGS@
+endif
+
 noinst_HEADERS = \
 		audiobuffer.h \
 		audio_input.h \

src/media/audio/echo-cancel/Makefile.am

@@ -13,10 +13,11 @@ endif
 if HAVE_WEBRTC_AP
 EC_SRC += webrtc_echo_canceller.cpp
 EC_HDR += webrtc_echo_canceller.h
+libecho_cancel_la_CXXFLAGS = @WEBRTC_CFLAGS@ $(AM_CXXFLAGS)
 endif
 
 libecho_cancel_la_SOURCES = \
-		$(EC_SRC)
+	$(EC_SRC)
 
 noinst_HEADERS = \
 	echo_canceller.h \