CMake: Add ucontext on Mac/OSX

CMakeLists.txt

@@ -50,6 +50,8 @@ if (APPLE)
     find_library(AUDIOTOOLBOX_LIBRARY AudioToolbox)
     find_library(AUDIOUNIT_LIBRARY AudioUnit)
     find_library(COCOA_LIBRARY Cocoa)
+
+    find_package(MacUcontext)
 endif (APPLE)
 
 if (MSVC)

cmake/FindMacUcontext.cmake

@@ -0,0 +1,23 @@
+include(CheckCXXSourceCompiles)
+
+check_cxx_source_compiles("
+#include <sys/ucontext.h>
+int main() {
+    ucontext_t context;
+#if defined(__x86_64__)
+    void *ptr = (void *) context.uc_mcontext->__ss.__rip;
+#elif defined(__i386)
+    void *ptr = (void *) context.uc_mcontext->__ss.__rip;
+#else
+#error Unknown arch
+#endif
+    return 0;
+}"
+    UCONTEXT_FOUND
+)
+
+if (UCONTEXT_FOUND)
+    add_compile_options(
+        -DWITH_UCONTEXT
+    )
+endif (UCONTEXT_FOUND)