Enable building libav without optimization

Some source files do not build with -O0 due to conflicting register
allocation and inline assembler constrains. We enforce optimization (O2)
for these files.

Also, I reduced the noise from warning messages induced by lazy handling
of "assignment discards ‘const’ qualifier" and "passing argument from
incompatible pointer type" in third-party sources.

libports/lib/mk/av.inc

@@ -1,6 +1,17 @@
 CC_C_OPT += -DHAVE_AV_CONFIG_H
 CC_C_OPT += -std=c99 -DPIC
 
+# The third-party sources induce a lot of "assignment discards ‘const’
+# qualifier" and "passing argument from incompatible pointer type" warnings.
+# Therefore, switch off _all_ warnings.
+CC_WARN += -w
+
+# Some source files do not build with -O0 due to conflicting register
+# allocation and inline assembler constrains. We enforce optimization for these
+# files.
+CC_OPT_h264_cabac = -O2
+CC_OPT_motion_est = -O2
+
 INC_DIR += $(REP_DIR)/src/lib/libav
 
 include $(REP_DIR)/src/lib/libav/config.mak

libports/lib/mk/avcodec.inc

@@ -2,8 +2,6 @@ include $(REP_DIR)/lib/mk/av.inc
 
 include $(REP_DIR)/lib/import/import-avcodec.mk
 
-CC_WARN += -Wno-pointer-sign -Wno-uninitialized -Wno-deprecated-declarations -Wno-switch
-
 LIBAVCODEC_DIR = $(REP_DIR)/contrib/$(LIBAV)/libavcodec
 
 include $(LIBAVCODEC_DIR)/Makefile

libports/lib/mk/avfilter.mk

@@ -2,8 +2,6 @@ include $(REP_DIR)/lib/mk/av.inc
 
 include $(REP_DIR)/lib/import/import-avfilter.mk
 
-CC_WARN += -Wno-pointer-sign -Wno-uninitialized -Wno-switch
-
 LIBAVFILTER_DIR = $(REP_DIR)/contrib/$(LIBAV)/libavfilter
 
 include $(LIBAVFILTER_DIR)/Makefile

libports/lib/mk/avformat.mk

@@ -2,8 +2,6 @@ include $(REP_DIR)/lib/mk/av.inc
 
 include $(REP_DIR)/lib/import/import-avformat.mk
 
-CC_WARN += -Wno-pointer-sign -Wno-deprecated-declarations
-
 LIBAVFORMAT_DIR = $(REP_DIR)/contrib/$(LIBAV)/libavformat
 
 include $(LIBAVFORMAT_DIR)/Makefile

libports/lib/mk/avutil.inc

@@ -2,8 +2,6 @@ include $(REP_DIR)/lib/mk/av.inc
 
 include $(REP_DIR)/lib/import/import-avutil.mk
 
-CC_WARN += -Wno-pointer-sign -Wno-switch -Wno-parentheses
-
 LIBAVUTIL_DIR = $(REP_DIR)/contrib/$(LIBAV)/libavutil
 
 include $(LIBAVUTIL_DIR)/Makefile