Add basic support for compiling on RISC OS

src/atomic/SDL_spinlock.c

@@ -32,6 +32,10 @@
 #include <atomic.h>
 #endif
 
+#if !defined(HAVE_GCC_ATOMICS) && defined(__RISCOS__)
+#include <unixlib/local.h>
+#endif
+
 #if defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
 #include <xmmintrin.h>
 #endif
@@ -84,6 +88,16 @@ SDL_AtomicTryLock(SDL_SpinLock *lock)
          defined(__ARM_ARCH_5__) || defined(__ARM_ARCH_5TE__) || \
          defined(__ARM_ARCH_5TEJ__))
     int result;
+
+#if defined(__RISCOS__)
+    if (__cpucap_have_rex()) {
+        __asm__ __volatile__ (
+            "ldrex %0, [%2]\nteq   %0, #0\nstrexeq %0, %1, [%2]"
+            : "=&r" (result) : "r" (1), "r" (lock) : "cc", "memory");
+        return (result == 0);
+    }
+#endif
+
     __asm__ __volatile__ (
         "swp %0, %1, [%2]\n"
         : "=&r,&r" (result) : "r,0" (1), "r,r" (lock) : "memory");

src/dynapi/SDL_dynapi.h

@@ -53,6 +53,8 @@
 #define SDL_DYNAMIC_API 0
 #elif defined(__PSP__) && __PSP__
 #define SDL_DYNAMIC_API 0
+#elif defined(__riscos__) && __riscos__ /* probably not useful on RISC OS, since dlopen() can't be used when using static linking. */
+#define SDL_DYNAMIC_API 0
 #elif defined(__clang_analyzer__)
 #define SDL_DYNAMIC_API 0  /* Turn off for static analysis, so reports are more clear. */
 #endif

src/thread/pthread/SDL_systhread.c

@@ -188,7 +188,7 @@ SDL_ThreadID(void)
 int
 SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
 {
-#if __NACL__ 
+#if __NACL__ || __RISCOS__
     /* FIXME: Setting thread priority does not seem to be supported in NACL */
     return 0;
 #elif __LINUX__