build: pass sysroot to MacOS SDK

There were issues with configuring LuaJIT on Apple machines, since
<LuaJITTestArch> CMake auxiliary routine fails to locate system headers
(e.g. assert.h in case when LUA_USE_ASSERT is enabled). As a result
platform detection fails and LuaJIT configuration ends with the fatal
error. This patch adds the necessary flags to help the routine to find
the required system headers.

Needed for tarantool/tarantool#6065
Relates to tarantool/tarantool#5629
Follows up tarantool/tarantool#4862

Reviewed-by: Sergey Kaplun <[email protected]>
Reviewed-by: Sergey Ostanevich <[email protected]>
Signed-off-by: Igor Munkin <[email protected]>

Author: igormunkin

cmake/LuaJITUtils.cmake

@@ -1,4 +1,17 @@
 function(LuaJITTestArch outvar strflags)
+  # XXX: This routine uses external headers (e.g. system ones),
+  # which location is specified either implicitly (within CMake
+  # machinery) or explicitly (manually by configuration options).
+  # Need -isysroot flag on recentish MacOS after command line
+  # tools no longer provide headers in /usr/include.
+  # XXX: According to CMake documentation[1], CMAKE_OSX_SYSROOT
+  # variable *should* be ignored on the platforms other than
+  # MacOS. It is ignored by CMake itself, but since this routine
+  # extends CMake, it should also follow this policy.
+  # [1]: https://cmake.org/cmake/help/v3.1/variable/CMAKE_OSX_SYSROOT.html
+  if(CMAKE_SYSTEM_NAME STREQUAL "Darwin" AND CMAKE_OSX_SYSROOT)
+    set(strflags "${strflags} -isysroot ${CMAKE_OSX_SYSROOT}")
+  endif()
   # XXX: <execute_process> simply splits the COMMAND argument by
   # spaces with no further parsing. At the same time GCC is bad in
   # argument handling, so let's help it a bit.