build: add a -Clean option to build.ps1

When the compiler changes, the SDK and tool builds do not notice the
compiler change due to the missing compiler tracking. This allows us to
quickly perform an incremental by not discarding the compiler build.

Author: compnerd

utils/build.ps1

@@ -62,6 +62,9 @@ If set, debug information will be generated for the builds.
 .PARAMETER EnableCaching
 If true, use `sccache` to cache the build rules.
 
+.PARAMETER Clean
+If true, clean non-compiler builds while building.
+
 .PARAMETER Test
 An array of names of projects to run tests for.
 '*' runs all tests
@@ -101,6 +104,7 @@ param(
   [string[]] $Test = @(),
   [string] $Stage = "",
   [string] $BuildTo = "",
+  [switch] $Clean,
   [switch] $DebugInfo,
   [switch] $EnableCaching,
   [switch] $ToBatch
@@ -1161,7 +1165,6 @@ function Build-Runtime($Arch) {
         SWIFT_NATIVE_SWIFT_TOOLS_PATH = "$BinaryCache\1\bin";
         SWIFT_PATH_TO_LIBDISPATCH_SOURCE = "$SourceCache\swift-corelibs-libdispatch";
         SWIFT_PATH_TO_STRING_PROCESSING_SOURCE = "$SourceCache\swift-experimental-string-processing";
-        SWIFT_PATH_TO_SWIFT_SYNTAX_SOURCE = "$SourceCache\swift-syntax";
         CMAKE_SHARED_LINKER_FLAGS = @("/INCREMENTAL:NO", "/OPT:REF", "/OPT:ICF");
       }
   }
@@ -1743,6 +1746,13 @@ if (-not $SkipBuild) {
   Invoke-BuildStep Build-Compilers $HostArch
 }
 
+if ($Clean) {
+  2..16 | % { Remove-Item -Force -Recurse "$BinaryCache\$_" -ErrorAction Ignore }
+  foreach ($Arch in $SDKArchs) {
+    0..3 | % { Remove-Item -Force -Recurse "$BinaryCache\$($Arch.BuildiD + $_)" -ErrorAction Ignore }
+  }
+}
+
 foreach ($Arch in $SDKArchs) {
   if (-not $SkipBuild) {
     Invoke-BuildStep Build-ZLib $Arch