libsndfile: enable external-libs (FLAC, Ogg, Opus and Vorbis)

create the pkg-config sndfile.pc used by fluidsynth and pulseaudio

packages/audio/libsndfile/package.mk

@@ -8,13 +8,20 @@ PKG_SHA256="8cdee0acb06bb0a3c1a6ca524575643df8b1f3a55a0893b4dd9f829d08263785"
 PKG_LICENSE="LGPL-2.1-or-later"
 PKG_SITE="https://libsndfile.github.io/libsndfile/"
 PKG_URL="https://github.com/libsndfile/libsndfile/archive/${PKG_VERSION}.tar.gz"
-PKG_DEPENDS_TARGET="toolchain alsa-lib"
+PKG_DEPENDS_TARGET="toolchain alsa-lib flac libogg libvorbis opus"
 PKG_LONGDESC="A C library for reading and writing sound files containing sampled audio data."
 PKG_BUILD_FLAGS="+pic"
 
+# As per notes in configure.ac:
+#  One or more of the external libraries (ie libflac, libogg, libvorbis and libopus)
+#  is either missing ... Unfortunately, for ease of maintenance, the external libs
+#  are an all or nothing affair.
+# So all of flac, libogg, libvorbis, opus are required.
+
 PKG_CMAKE_OPTS_TARGET="-DBUILD_PROGRAMS=OFF \
                        -DBUILD_EXAMPLES=OFF \
-                       -DBUILD_TESTING=OFF \
                        -DBUILD_REGTEST=OFF \
-                       -DENABLE_EXTERNAL_LIBS=OFF \
-                       -DINSTALL_MANPAGES=OFF"
+                       -DBUILD_TESTING=OFF \
+                       -DENABLE_EXTERNAL_LIBS=ON \
+                       -DINSTALL_MANPAGES=OFF \
+                       -DINSTALL_PKGCONFIG_MODULE=ON"

packages/audio/libsndfile/patches/libsndfile-add-required-static-libaries-to-pkg-config.patch

@@ -0,0 +1,9 @@
+--- a/sndfile.pc	2021-01-24 23:22:23.000000000 +1100
++++ b/sndfile.pc.in	2021-09-12 14:30:47.763655089 +1000
+@@ -8,5 +8,5 @@
+ Requires:
+ Requires.private: @EXTERNAL_XIPH_REQUIRE@
+ Version: @VERSION@
+-Libs: -L${libdir} -lsndfile
++Libs: -L${libdir} -lsndfile -lFLAC -logg -lvorbis -lvorbisenc -lopus
+ Cflags: -I${includedir}