[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.

Author: bnbarham

utils/build-presets.ini

@@ -890,11 +890,6 @@ installable-package=%(installable_package)s
 # in Linux CI bots
 relocate-xdg-cache-home-under-build-subdir
 
-# Temporarily disable early swift driver/syntax builds so that linux images
-# can use the swift release images as a base.
-skip-early-swift-driver
-skip-early-swiftsyntax
-
 [preset: buildbot_linux_base]
 mixin-preset=
     mixin_linux_installation
@@ -1149,11 +1144,6 @@ reconfigure
 # in Linux CI bots
 relocate-xdg-cache-home-under-build-subdir
 
-# Temporarily disable early swift driver/syntax builds so that linux images
-# can use the swift release images as a base.
-skip-early-swift-driver
-skip-early-swiftsyntax
-
 [preset: buildbot_incremental_linux]
 mixin-preset=
     buildbot_incremental_linux_base

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 '\