build: add a CMake based build for Windows

Given that swift-package-manager is not currently ready for Windows,
this addition makes it possible to build for Windows.

CMakeLists.txt

@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.16)
+
+list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules)
+
+project(swift-log
+  LANGUAGES Swift)
+
+set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/swift)
+
+include(SwiftSupport)
+
+add_subdirectory(Sources)
+
+export(EXPORT swift-log
+  NAMESPACE SwiftLog::
+  FILE swift-log-config.cmake)

Sources/CMakeLists.txt

@@ -0,0 +1 @@
+add_subdirectory(Logging)

Sources/Logging/CMakeLists.txt

@@ -0,0 +1,21 @@
+add_library(Logging
+  Locks.swift
+  Logging.swift
+  LogHandler.swift)
+target_compile_options(Logging PRIVATE
+  "SHELL:$<$<PLATFORM_ID:Windows>:-Xcc -D_CRT_SECURE_NO_WARNINGS>")
+set_target_properties(Logging PROPERTIES
+  INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_Swift_MODULE_DIRECTORY})
+
+
+install(TARGETS Logging
+  EXPORT swift-log
+  ARCHIVE DESTINATION lib/swift$<$<NOT:$<BOOL:${BUILD_SHARED_LIBS}>>:_static>/$<LOWER_CASE:${CMAKE_SYSTEM_NAME}>
+  LIBRARY DESTINATION lib/swift$<$<NOT:$<BOOL:${BUILD_SHARED_LIBS}>>:_static>/$<LOWER_CASE:${CMAKE_SYSTEM_NAME}>
+  RUNTIME DESTINATION bin)
+get_swift_host_arch(swift_arch)
+install(FILES
+  EXPORT swift-log
+  $<TARGET_PROPERTY:Logging,Swift_MODULE_DIRECTORY>/Logging.swiftdoc
+  $<TARGET_PROPERTY:Logging,Swift_MODULE_DIRECTORY>/Logging.swiftmodule
+  DESTINATION lib/swift$<$<NOT:$<BOOL:${BUILD_SHARED_LIBS}>>:_static>/$<LOWER_CASE:${CMAKE_SYSTEM_NAME}>/${swift_arch})

cmake/modules/SwiftSupport.cmake

@@ -0,0 +1,37 @@
+
+# Returns the current architecture name in a variable
+#
+# Usage:
+#   get_swift_host_arch(result_var_name)
+#
+# If the current architecture is supported by Swift, sets ${result_var_name}
+# with the sanitized host architecture name derived from CMAKE_SYSTEM_PROCESSOR.
+function(get_swift_host_arch result_var_name)
+  if("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "x86_64")
+    set("${result_var_name}" "x86_64" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "aarch64")
+    set("${result_var_name}" "aarch64" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "ppc64")
+    set("${result_var_name}" "powerpc64" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "ppc64le")
+    set("${result_var_name}" "powerpc64le" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "s390x")
+    set("${result_var_name}" "s390x" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "armv6l")
+    set("${result_var_name}" "armv6" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "armv7l")
+    set("${result_var_name}" "armv7" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "armv7-a")
+    set("${result_var_name}" "armv7" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "AMD64")
+    set("${result_var_name}" "x86_64" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "IA64")
+    set("${result_var_name}" "itanium" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "x86")
+    set("${result_var_name}" "i686" PARENT_SCOPE)
+  elseif("${CMAKE_SYSTEM_PROCESSOR}" STREQUAL "i686")
+    set("${result_var_name}" "i686" PARENT_SCOPE)
+  else()
+    message(FATAL_ERROR "Unrecognized architecture on host system: ${CMAKE_SYSTEM_PROCESSOR}")
+  endif()
+endfunction()