Add USE_INTERNAL_LIBS, a default for USE_INTERNAL_*

Linux distributions that want to link dependencies externally will
generally want to link (almost) every dependency externally; similarly,
minimal-dependency builds that want to use the embedded copies of
dependencies will generally want to do so for (almost) every dependency.
Make it easier to choose one of those by setting USE_INTERNAL_LIBS=0
or USE_INTERNAL_LIBS=1, respectively.

The default can still be overridden per-dependency; for instance,
"make USE_INTERNAL_LIBS=0 USE_INTERNAL_OPUS=1" will use the system
version of everything except Opus.

Makefile

@@ -187,28 +187,32 @@ ifndef USE_FREETYPE
 USE_FREETYPE=0
 endif
 
+ifndef USE_INTERNAL_LIBS
+USE_INTERNAL_LIBS=1
+endif
+
 ifndef USE_INTERNAL_SPEEX
-USE_INTERNAL_SPEEX=1
+USE_INTERNAL_SPEEX=$(USE_INTERNAL_LIBS)
 endif
 
 ifndef USE_INTERNAL_OGG
-USE_INTERNAL_OGG=1
+USE_INTERNAL_OGG=$(USE_INTERNAL_LIBS)
 endif
 
 ifndef USE_INTERNAL_OPUS
-USE_INTERNAL_OPUS=1
+USE_INTERNAL_OPUS=$(USE_INTERNAL_LIBS)
 endif
 
 ifndef USE_INTERNAL_ZLIB
-USE_INTERNAL_ZLIB=1
+USE_INTERNAL_ZLIB=$(USE_INTERNAL_LIBS)
 endif
 
 ifndef USE_INTERNAL_JPEG
-USE_INTERNAL_JPEG=1
+USE_INTERNAL_JPEG=$(USE_INTERNAL_LIBS)
 endif
 
 ifndef USE_LOCAL_HEADERS
-USE_LOCAL_HEADERS=1
+USE_LOCAL_HEADERS=$(USE_INTERNAL_LIBS)
 endif
 
 ifndef USE_RENDERER_DLOPEN

README

@@ -97,6 +97,10 @@ Makefile.local:
   USE_CODEC_OPUS     - enable Ogg Opus support
   USE_MUMBLE         - enable Mumble support
   USE_VOIP           - enable built-in VoIP support
+  USE_INTERNAL_LIBS  - build internal libraries instead of dynamically
+                       linking against system libraries; this just sets
+		       the default for USE_INTERNAL_SPEEX etc.
+		       and USE_LOCAL_HEADERS
   USE_INTERNAL_SPEEX - build internal speex library instead of dynamically
                        linking against system libspeex
   USE_FREETYPE       - enable FreeType support for rendering fonts