GHA: specify Swift compile target, C++ compiler, install location

Add missing flags for swift-testing configuration. This is primarily the
C++ compiler, target triple, and the install location.

Author: compnerd

.github/workflows/swift-toolchain.yml

@@ -2126,7 +2126,12 @@ jobs:
                 -D BUILD_SHARED_LIBS=YES `
                 -D CMAKE_BUILD_TYPE=Release `
                 -D CMAKE_BUILD_WITH_INSTALL_RPATH=YES `
+                -D CMAKE_CXX_COMPILER=${{ matrix.cxx }} `
+                -D CMAKE_CXX_COMPILER_TARGET=${{ matrix.triple }} `
+                -D CMAKE_CXX_FLAGS="${{ matrix.cxxflags }}" `
+                -D CMAKE_INSTALL_PREFIX=${{ github.workspace }}/BuildRoot/Library/Developer/Platforms/${{ matrix.os }}.platform/Developer/Library/Testing-development/usr `
                 -D CMAKE_Swift_COMPILER=${SWIFTC} `
+                -D CMAKE_Swift_COMPILER_TARGET=${{ matrix.triple_no_api_level }} `
                 -D CMAKE_Swift_FLAGS="-resource-dir ${{ github.workspace }}/BinaryCache/Library/Developer/Platforms/${{ matrix.os }}.platform/Developer/SDKs/${{ matrix.os }}.sdk/usr/lib/swift -L${{ github.workspace }}/BinaryCache/Library/Developer/Platforms/${{ matrix.os }}.platform/Developer/SDKs/${{ matrix.os }}.sdk/usr/lib/swift/${{ matrix.os }} ${OVERLAY_FLAGS} ${{ matrix.swiftflags }}" `
                 -D CMAKE_Swift_FLAGS_RELEASE="-O" `
                 -D CMAKE_SYSTEM_NAME=${{ matrix.os }} `