alsa-lib: add patch to fix incorrect code dependency

This commit adds a patch to alsa-lib that fixes an incorrect code
dependency: some code built when MIDI support is enabled is
unconditionally referencing code that is built when SEQ support is
enabled, both options being independent.

This causes build failures such as:

/home/buildroot/buildroot-test/instance-1/output/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libasound.a(pcm_dmix.o): In function `snd_pcm_dmix_sync_ptr':
pcm_dmix.c:(.text+0x83c): warning:
/home/buildroot/buildroot-test/instance-1/output/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libasound.a(rawmidi_symbols.o):(.data+0x4): undefined reference to `_snd_module_rawmidi_virt'

Fixes:

  http://autobuild.buildroot.net/results/5964e7028c31a8f75b38a27270410f0b3c5c8422/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
[Arnout: add upstream link to the patch]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/alsa-lib/0005-src-rawmidi-rawmidi_symbols.c-use-rawmidi_virt-only-.patch

@@ -0,0 +1,52 @@
+From da16e18f03fc63e1206b93d6a719b177d4f4bb99 Mon Sep 17 00:00:00 2001
+From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+Date: Fri, 11 Aug 2017 22:33:01 +0200
+Subject: [PATCH] src/rawmidi/rawmidi_symbols.c: use rawmidi_virt only when
+ available
+
+src/rawmidi/Makefile.am only brings rawmidi_virt.c into the build when
+BUILD_SEQ is defined (i.e when --enable-seq is passed). However,
+rawmidi_symbols.c unconditionally refers to _snd_module_rawmidi_virt,
+defined in rawmidi_virt.c.
+
+This causes a link failure when BUILD_SEQ is disabled. For example
+when linking ffmpeg against alsa-lib:
+
+/home/thomas/projets/buildroot/output/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libasound.a(pcm_dmix.o): In function `snd_pcm_dmix_sync_ptr':
+pcm_dmix.c:(.text+0x83c): warning:
+/home/thomas/projets/buildroot/output/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libasound.a(rawmidi_symbols.o):(.data+0x4): undefined reference to `_snd_module_rawmidi_virt'
+collect2: error: ld returned 1 exit status
+
+To fix this, we make sure that rawmidi_symbols.c only uses
+_snd_module_rawmidi_virt when available.
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+
+Patch sent upstream: https://www.spinics.net/lists/alsa-devel/msg65902.html
+---
+ src/rawmidi/rawmidi_symbols.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/src/rawmidi/rawmidi_symbols.c b/src/rawmidi/rawmidi_symbols.c
+index cdc06d7..6473433 100644
+--- a/src/rawmidi/rawmidi_symbols.c
++++ b/src/rawmidi/rawmidi_symbols.c
+@@ -21,11 +21,15 @@
+ #ifndef PIC
+ 
+ extern const char *_snd_module_rawmidi_hw;
++#ifdef BUILD_SEQ
+ extern const char *_snd_module_rawmidi_virt;
++#endif
+ 
+ static const char **snd_rawmidi_open_objects[] = {
+ 	&_snd_module_rawmidi_hw,
++#ifdef BUILD_SEQ
+ 	&_snd_module_rawmidi_virt
++#endif
+ };
+ 	
+ void *snd_rawmidi_open_symbols(void)
+-- 
+2.9.4
+