Update WindowsBuild.md

Add instructions to enable tests on Windows.  This requires additional patches to libdispatch and Foundation to enable the build as well as run.  But, this is in preparation for those changes to get merged and for others to replicate the test suite.

Author: compnerd

docs/WindowsBuild.md

@@ -280,6 +280,7 @@ cmake -G Ninja^
   -DCMAKE_SWIFT_COMPILER=S:\b\swift\bin\swiftc.exe^
   -DCURL_LIBRARY="S:/curl/builds/libcurl-vc15-x64-release-static-ipv6-sspi-winssl/lib/libcurl_a.lib"^
   -DCURL_INCLUDE_DIR="S:/curl/builds/libcurl-vc15-x64-release-static-ipv6-sspi-winssl/include"^
+  -DENABLE_TESTING=NO^
   -DICU_ROOT="S:/thirdparty/icu4c-63_1-Win64-MSVC2017"^
   -DLIBXML2_LIBRARY="S:/libxml2/win32/bin.msvc/libxml2_a.lib"^
   -DLIBXML2_INCLUDE_DIR="S:/libxml2/include"^
@@ -288,7 +289,6 @@ cmake -G Ninja^
    S:\swift-corelibs-foundation
  popd
  cmake --build S:\b\foundation
-
 ```
 
 - Add Foundation to your path:
@@ -321,7 +321,43 @@ cmake --build S:\b\xctest
 path S:\b\xctest;%PATH%
 ```
 
-### 15. Install Swift on Windows
+### 15. Test XCTest
+
+```cmd
+ninja -C S:\b\xctest check-xctest
+```
+
+### 16. Rebuild Foundation
+
+```cmd
+mkdir "S:\b\foundation"
+pushd "S:\b\foundation
+cmake -G Ninja^
+  -DCMAKE_BUILD_TYPE=RelWithDebInfo^
+  -DCMAKE_C_COMPILER=clang-cl^
+  -DCMAKE_SWIFT_COMPILER=S:\b\swift\bin\swiftc.exe^
+  -DCURL_LIBRARY="S:/curl/builds/libcurl-vc15-x64-release-static-ipv6-sspi-winssl/lib/libcurl_a.lib"^
+  -DCURL_INCLUDE_DIR="S:/curl/builds/libcurl-vc15-x64-release-static-ipv6-sspi-winssl/include"^
+  -DENABLE_TESTING=YES^
+  -DICU_ROOT="S:/thirdparty/icu4c-63_1-Win64-MSVC2017"^
+  -DLIBXML2_LIBRARY="S:/libxml2/win32/bin.msvc/libxml2_a.lib"^
+  -DLIBXML2_INCLUDE_DIR="S:/libxml2/include"^
+  -DFOUNDATION_PATH_TO_LIBDISPATCH_SOURCE=S:\swift-corelibs-libdispatch^
+  -DFOUNDATION_PATH_TO_LIBDISPATCH_BUILD=S:\b\libdispatch^
+  -DFOUNDATION_PATH_TO_XCTEST_BUILD=S:\b\xctest^
+   S:\swift-corelibs-foundation
+ popd
+ cmake --build S:\b\foundation
+```
+
+### 17. Test Foundation
+
+```cmd
+cmake --build S:\b\foundation
+ninja -C S:\b\foundation test 
+```
+
+### 18. Install Swift on Windows
 
 - Run ninja install: