Auto detect OSX_SYSROOT for macos >= 10.14 (#2470)

* Auto detect OSX_SYSROOT for macos >= 10.14

* Fix potential regex issue.

CMakeLists.txt

@@ -40,8 +40,8 @@ include(var_functions)
 
 NGRAPH_GET_VERSION_LABEL()
 
-string(REGEX MATCH "([0-9?]+)\.([0-9?]+)\.([0-9?]+)" NGRAPH_VERSION_SHORT "${NGRAPH_VERSION_LABEL}")
-string(REGEX MATCH "([0-9?]+)\.([0-9?]+)" NGRAPH_API_VERSION "${NGRAPH_VERSION_LABEL}")
+string(REGEX MATCH "([0-9?]+)\\.([0-9?]+)\\.([0-9?]+)" NGRAPH_VERSION_SHORT "${NGRAPH_VERSION_LABEL}")
+string(REGEX MATCH "([0-9?]+)\\.([0-9?]+)" NGRAPH_API_VERSION "${NGRAPH_VERSION_LABEL}")
 string(REGEX MATCH "[^v](.*)" NGRAPH_VERSION "${NGRAPH_VERSION_LABEL}")
 string(REPLACE "." ";" NGRAPH_VERSION_PARTS "${NGRAPH_VERSION_SHORT}")
 list(GET NGRAPH_VERSION_PARTS 0 NGRAPH_VERSION_MAJOR)
@@ -76,6 +76,31 @@ if ("${CMAKE_GENERATOR}" MATCHES "^Visual Studio.*$")
     set(MSVS TRUE)
 endif()
 
+if (APPLE AND (NOT CMAKE_OSX_SYSROOT))
+    execute_process(COMMAND sw_vers -productVersion
+        OUTPUT_VARIABLE OSX_FULL_VERSION
+        OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+    string(REGEX REPLACE "^([0-9]+\\.[0-9]+).*$" "\\1"
+        OSX_SHORT_VERSION "${OSX_FULL_VERSION}")
+
+    if(NOT (OSX_SHORT_VERSION VERSION_LESS 10.14))
+        # Xcode is installed
+        set(XCODE_ISYSROOT /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX${OSX_SHORT_VERSION}.sdk)
+        message(STATUS "Trying Xcode sdk at ${XCODE_ISYSROOT}.")
+        if(NOT EXISTS ${XCODE_ISYSROOT})
+            # Command line tools only
+            set(XCODE_ISYSROOT /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk)
+            message(STATUS "Trying command line tool sdk at ${XCODE_ISYSROOT}.")
+            if(NOT EXISTS ${XCODE_ISYSROOT})
+                message(FATAL_ERROR "Cannot find macos sdk.")
+            endif()
+        endif()
+        message(STATUS "Setting CMAKE_OSX_SYSROOT for macos ${OSX_SHORT_VERSION} to ${XCODE_ISYSROOT}")
+        set(CMAKE_OSX_SYSROOT ${XCODE_ISYSROOT})
+    endif()
+endif()
+
 # Setup CMAKE_ARGS to be forwarded to External Projects
 set(NGRAPH_FORWARD_CMAKE_ARGS
         -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}