[CMake] Move setting of OSX_SYSROOT before project().

According to the documentation, any OSX_SYSROOT needs to be set before
the first project call.
https://cmake.org/cmake/help/latest/variable/CMAKE_OSX_SYSROOT.html

Since the setting came too late, homebrew compilers were missing the
include list for homebrew compilers was generated wrongly.

Author: hageboeck

CMakeLists.txt

@@ -12,6 +12,19 @@ if(WIN32)
   cmake_policy(SET CMP0091 OLD)
   set(CMAKE_SKIP_TEST_ALL_DEPENDENCY TRUE)
 endif()
+if(APPLE AND (NOT CMAKE_OSX_SYSROOT OR CMAKE_OSX_SYSROOT STREQUAL ""))
+  # The SYSROOT *must* be set before the project() call
+  execute_process(COMMAND xcrun --sdk macosx --show-sdk-path
+    OUTPUT_VARIABLE SDK_PATH
+    ERROR_QUIET
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+  if(NOT EXISTS "${SDK_PATH}")
+    message(FATAL_ERROR "Could not detect macOS SDK path")
+  endif()
+
+  set(CMAKE_OSX_SYSROOT "${SDK_PATH}" CACHE PATH "SDK path" FORCE)
+endif()
 
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT ALLOW_IN_SOURCE)
   message(FATAL_ERROR

cmake/modules/SetUpMacOS.cmake

@@ -13,20 +13,6 @@ if (CMAKE_SYSTEM_NAME MATCHES Darwin)
     set(libcxx ON CACHE BOOL "Build using libc++" FORCE)
   endif()
 
-  if(NOT CMAKE_OSX_SYSROOT OR CMAKE_OSX_SYSROOT STREQUAL "")
-    execute_process(COMMAND xcrun --sdk macosx --show-sdk-path
-      OUTPUT_VARIABLE SDK_PATH
-      ERROR_QUIET
-      OUTPUT_STRIP_TRAILING_WHITESPACE)
-
-    if(NOT EXISTS "${SDK_PATH}")
-      message(FATAL_ERROR "Could not detect macOS SDK path")
-    endif()
-
-    set(CMAKE_OSX_SYSROOT "${SDK_PATH}" CACHE PATH "SDK path" FORCE)
-  endif()
-  message(STATUS "Using SDK path: ${CMAKE_OSX_SYSROOT}")
-
   #TODO: check haveconfig and rpath -> set rpath true
   #TODO: check Thread, define link command
   #TODO: more stuff check configure script