Meta: Fix compilation flags for clang-cl

As part of https://github.com/LadybirdWebBrowser/ladybird/issues/38 -
the first baby step, is to make sure that we do not use compile flags
not supported by clang-cl.

Meta/CMake/common_compile_options.cmake

@@ -5,17 +5,25 @@ set(CMAKE_CXX_EXTENSIONS OFF)
 
 set(CMAKE_COLOR_DIAGNOSTICS ON)
 
-add_compile_options(-Wall)
-add_compile_options(-Wextra)
+if (MSVC)
+    add_compile_options(/W4)
+    # do not warn about unused function
+    add_compile_options(/wd4505)
+    # disable exceptions
+    add_compile_options(/EHsc)
+    # disable floating-point expression contraction
+    add_compile_options(/fp:precise)
+else()
+    add_compile_options(-Wall -Wextra)
+    add_compile_options(-fno-exceptions)
+    add_compile_options(-ffp-contract=off)
+endif()
 
 add_compile_options(-Wno-invalid-offsetof)
 
 add_compile_options(-Wno-unknown-warning-option)
 add_compile_options(-Wno-unused-command-line-argument)
 
-add_compile_options(-fno-exceptions)
-
-add_compile_options(-ffp-contract=off)
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "18")
     add_compile_options(-Wpadded-bitfield)
@@ -27,7 +35,7 @@ if (NOT CMAKE_HOST_SYSTEM_NAME MATCHES SerenityOS)
     add_compile_options(-Werror)
 endif()
 
-if (CMAKE_CXX_COMPILER_ID MATCHES "Clang$")
+if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT CMAKE_CXX_SIMULATE_ID  MATCHES "MSVC")
     # Clang's default constexpr-steps limit is 1048576(2^20), GCC doesn't have one
     add_compile_options(-fconstexpr-steps=16777216)
 
@@ -41,6 +49,13 @@ elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
 
     # FIXME: This warning seems useful but has too many false positives with GCC 13.
     add_compile_options(-Wno-dangling-reference)
+elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang$" AND CMAKE_CXX_SIMULATE_ID MATCHES "MSVC")
+    add_compile_options(-Wno-reserved-identifier)
+    add_compile_options(-Wno-user-defined-literals)
+    add_definitions(-D_CRT_SECURE_NO_WARNINGS)
+
+    # TODO: this seems wrong, but we use this kind of code too much
+    # add_compile_options(-Wno-unsafe-buffer-usage)
 endif()
 
 if (UNIX AND NOT APPLE AND NOT ENABLE_FUZZERS)

Meta/CMake/lagom_compile_options.cmake

@@ -2,8 +2,17 @@ include(${CMAKE_CURRENT_LIST_DIR}/common_compile_options.cmake)
 
 add_compile_options(-Wno-maybe-uninitialized)
 add_compile_options(-Wno-shorten-64-to-32)
-add_compile_options(-fsigned-char)
-add_compile_options(-ggnu-pubnames)
+
+if(NOT MSVC)
+    add_compile_options(-fsigned-char)
+    add_compile_options(-ggnu-pubnames)
+else()
+    # char is signed
+    add_compile_options(/J)
+    # full symbolic debugginng information
+    add_compile_options(/Z7)
+endif()
+
 if (NOT WIN32)
     add_compile_options(-fPIC)
 endif()
@@ -13,7 +22,9 @@ if (LINUX)
 endif()
 
 if (CMAKE_BUILD_TYPE STREQUAL "Debug")
-    add_compile_options(-ggdb3)
+    if (NOT MSVC)
+        add_compile_options(-ggdb3)
+    endif()
     add_compile_options(-Og)
 else()
     add_compile_options(-O2)