[Build] Skip early-* on non-darwin hosts

These builds do not work outside of darwin currently. Rather than adding
the skip to all the necessary build presets, just disable in the product
instead.

(cherry picked from commit 2c42a38)

Author: bnbarham

utils/swift_build_support/swift_build_support/products/earlyswiftdriver.py

@@ -42,6 +42,11 @@ def is_before_build_script_impl_product(cls):
         return True
 
     def should_build(self, host_target):
+        # Temporarily disable for non-darwin since this build never works
+        # outside of that case currently.
+        if sys.platform != 'darwin':
+            return False
+
         if self.is_cross_compile_target(host_target):
             return False
 

utils/swift_build_support/swift_build_support/products/earlyswiftsyntax.py

@@ -32,6 +32,11 @@ def is_before_build_script_impl_product(cls):
         return True
 
     def should_build(self, host_target):
+        # Temporarily disable for non-darwin since this build never works
+        # outside of that case currently.
+        if sys.platform != 'darwin':
+            return False
+
         if self.args.build_early_swiftsyntax:
             if toolchain.host_toolchain().find_tool("swift") is None:
                 warn_msg = 'Host toolchain could not locate a '\