sdl2: fix build with --disable-threads

SDL_LinuxSetThreadPriority() has been added since version 2.0.9 and
https://github.com/SDL-mirror/SDL/commit/f25a7fa870bdceb339e5105973f689606bcb9086

However, this function is used in src/dynapi/SDL_dynapi_procs.h even
when SDL_THREADS_DISABLED

However, when SDL_THREADS_DISABLED is set, SDL_LinuxSetThreadPriority is
not defined because thread/pthread/SDL_systhread.c is not built

So check SDL_THREADS_DISABLED in addition to __LINUX__

Fixes:
 - http://autobuild.buildroot.org/results/539cb9ab6c605dc6be73ebe90debab1a998f2451

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/sdl2/0001-fix-build-with-disable-threads.patch

@@ -0,0 +1,63 @@
+From 26646028f79d7f3d857df9b46cd6d0285796c699 Mon Sep 17 00:00:00 2001
+From: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+Date: Wed, 21 Nov 2018 22:31:09 +0100
+Subject: [PATCH] fix build with --disable-threads
+
+SDL_LinuxSetThreadPriority() has been added since version 2.0.9 and
+https://github.com/SDL-mirror/SDL/commit/f25a7fa870bdceb339e5105973f689606bcb9086
+
+However, this function is used in src/dynapi/SDL_dynapi_procs.h even
+when SDL_THREADS_DISABLED
+
+However, when SDL_THREADS_DISABLED is set, SDL_LinuxSetThreadPriority is
+not defined because thread/pthread/SDL_systhread.c is not built
+
+So check SDL_THREADS_DISABLED in addition to __LINUX__
+
+Fixes:
+ - http://autobuild.buildroot.org/results/539cb9ab6c605dc6be73ebe90debab1a998f2451
+
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ include/SDL_system.h          | 4 ++--
+ src/dynapi/SDL_dynapi_procs.h | 2 +-
+ 2 files changed, 3 insertions(+), 3 deletions(-)
+
+diff --git a/include/SDL_system.h b/include/SDL_system.h
+index 4dc372d6b..0513d7fa5 100644
+--- a/include/SDL_system.h
++++ b/include/SDL_system.h
+@@ -77,7 +77,7 @@ extern DECLSPEC SDL_bool SDLCALL SDL_DXGIGetOutputInfo( int displayIndex, int *a
+ 
+ 
+ /* Platform specific functions for Linux */
+-#ifdef __LINUX__
++#if defined(__LINUX__) && !defined(SDL_THREADS_DISABLED)
+ 
+ /**
+    \brief Sets the UNIX nice value for a thread, using setpriority() if possible, and RealtimeKit if available.
+@@ -86,7 +86,7 @@ extern DECLSPEC SDL_bool SDLCALL SDL_DXGIGetOutputInfo( int displayIndex, int *a
+  */
+ extern DECLSPEC int SDLCALL SDL_LinuxSetThreadPriority(Sint64 threadID, int priority);
+  
+-#endif /* __LINUX__ */
++#endif /* defined(__LINUX__) && !defined(SDL_THREADS_DISABLED) */
+ 	
+ /* Platform specific functions for iOS */
+ #if defined(__IPHONEOS__) && __IPHONEOS__
+diff --git a/src/dynapi/SDL_dynapi_procs.h b/src/dynapi/SDL_dynapi_procs.h
+index c95cf708b..ee9bf60a6 100644
+--- a/src/dynapi/SDL_dynapi_procs.h
++++ b/src/dynapi/SDL_dynapi_procs.h
+@@ -708,7 +708,7 @@ SDL_DYNAPI_PROC(SDL_bool,SDL_IsAndroidTV,(void),(),return)
+ SDL_DYNAPI_PROC(double,SDL_log10,(double a),(a),return)
+ SDL_DYNAPI_PROC(float,SDL_log10f,(float a),(a),return)
+ SDL_DYNAPI_PROC(char*,SDL_GameControllerMappingForDeviceIndex,(int a),(a),return)
+-#ifdef __LINUX__
++#if defined(__LINUX__) && !defined(SDL_THREADS_DISABLED)
+ SDL_DYNAPI_PROC(int,SDL_LinuxSetThreadPriority,(Sint64 a, int b),(a,b),return)
+ #endif
+ SDL_DYNAPI_PROC(SDL_bool,SDL_HasAVX512F,(void),(),return)
+-- 
+2.17.1
+