Revert "Fallback to building Cmake from source on all platforms, not just Linux (swiftlang#33543)"

This reverts commit 539b241.

Author: CodaFi

utils/swift_build_support/swift_build_support/cmake.py

@@ -18,6 +18,7 @@
 from __future__ import absolute_import, unicode_literals
 
 import os
+import platform
 import re
 from numbers import Number
 
@@ -255,6 +256,9 @@ def build_cmake(self, source_root, build_root):
     # the source and build the source if necessary. Returns the path to the
     # cmake binary.
     def check_cmake_version(self, source_root, build_root):
+        if platform.system() != 'Linux':
+            return
+
         cmake_source_dir = os.path.join(source_root, 'cmake')
         # If the source is not checked out then don't attempt to build cmake.
         if not os.path.isdir(cmake_source_dir):