[android] Detect the NDK version by reading source.properties, not by checking the NDK name

Author: finagolfin

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -555,15 +555,22 @@ function(_add_target_variant_link_flags)
     list(APPEND link_libraries "dl" "log")
     # We need to add the math library, which is linked implicitly by libc++
     list(APPEND result "-lm")
-    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows)
+    if(NOT CMAKE_HOST_SYSTEM MATCHES Windows AND NOT "${SWIFT_ANDROID_NDK_PATH}" STREQUAL "")
       # The Android resource dir is specified from build.ps1 on windows.
-      if(NOT "${SWIFT_ANDROID_NDK_PATH}" STREQUAL "")
-        if("${SWIFT_ANDROID_NDK_PATH}" MATCHES "r26|r27")
+      if(EXISTS "${SWIFT_ANDROID_NDK_PATH}/source.properties")
+        file(READ "${SWIFT_ANDROID_NDK_PATH}/source.properties" NDK_VERSION)
+        if(NOT NDK_VERSION MATCHES "Pkg\\.Revision = ([0-9\\.]+)")
+          message(FATAL_ERROR "Could not find NDK version in source.properties: ${NDK_VERSION}")
+        endif()
+
+        if("${CMAKE_MATCH_1}" VERSION_GREATER_EQUAL "26")
           file(GLOB RESOURCE_DIR ${SWIFT_SDK_ANDROID_ARCH_${LFLAGS_ARCH}_PATH}/../lib/clang/*)
         else()
           file(GLOB RESOURCE_DIR ${SWIFT_SDK_ANDROID_ARCH_${LFLAGS_ARCH}_PATH}/../lib64/clang/*)
         endif()
         list(APPEND result "-resource-dir=${RESOURCE_DIR}")
+      else()
+        message(FATAL_ERROR "Could not detect NDK version: ${SWIFT_ANDROID_NDK_PATH}/source.properties not found")
       endif()
     endif()