Switch swift-system to build statically

This matches upstream `build.ps1` behavior.

Author: Steelskin

.github/workflows/swift-toolchain.yml

@@ -3106,7 +3106,7 @@ jobs:
           $SWIFTC = cygpath -m ${{ github.workspace }}/BinaryCache/Library/Developer/Toolchains/${{ inputs.swift_version }}+Asserts/usr/bin/swiftc.exe
 
           cmake -B ${{ github.workspace }}/BinaryCache/swift-system `
-                -D BUILD_SHARED_LIBS=YES `
+                -D BUILD_SHARED_LIBS=NO `
                 -D BUILD_TESTING=NO `
                 -D CMAKE_BUILD_TYPE=Release `
                 -D CMAKE_C_COMPILER=${CLANG_CL} `