CMake: Add DISABLE_SSE4 option

NOT recommended. Only if you ABSOLUTELY need it.

The SSE2/legacy build will be a separate download option, and
warn you if you try to run it on a CPU that supports SSE4.

CMakeModules/DuckStationBuildOptions.cmake

@@ -5,6 +5,7 @@ option(BUILD_NOGUI_FRONTEND "Build the NoGUI frontend" OFF)
 option(BUILD_QT_FRONTEND "Build the Qt frontend" ON)
 option(BUILD_REGTEST "Build regression test runner" OFF)
 option(BUILD_TESTS "Build unit tests" OFF)
+option(DISABLE_SSE4 "Build with SSE4 instructions disabled, reduces performance" OFF)
 
 if(LINUX OR BSD)
   option(ENABLE_X11 "Support X11 window system" ON)

CMakeModules/DuckStationBuildSummary.cmake

@@ -38,8 +38,7 @@ It does **not** use the LSB subdirectories of bin, share, etc, so you should dis
 endif()
 
 if(NOT IS_SUPPORTED_COMPILER)
-  message(WARNING "
-*************** UNSUPPORTED CONFIGURATION ***************
+  message(WARNING "*************** UNSUPPORTED CONFIGURATION ***************
 You are not compiling DuckStation with a supported compiler.
 It may not even build successfully.
 DuckStation only supports the Clang and MSVC compilers.
@@ -48,11 +47,18 @@ No support will be provided, continue at your own risk.
 endif()
 
 if(WIN32)
-  message(WARNING "
-*************** UNSUPPORTED CONFIGURATION ***************
+  message(WARNING "*************** UNSUPPORTED CONFIGURATION ***************
 You are compiling DuckStation with CMake on Windows.
 It may not even build successfully.
 DuckStation only supports MSBuild on Windows.
 No support will be provided, continue at your own risk.
 *********************************************************")
 endif()
+
+if(CPU_ARCH_X64 AND DISABLE_SSE4)
+  message(WARNING "*********************** WARNING ***********************
+SSE4 instructions are disabled. This will result in
+reduced performance. You should not enable this option
+unless you have a pre-2008 CPU.
+*******************************************************")
+endif()

CMakeModules/DuckStationUtils.cmake

@@ -69,7 +69,7 @@ function(detect_architecture)
          CMAKE_SIZEOF_VOID_P EQUAL 8)
     message(STATUS "Building x86_64 binaries.")
     set(CPU_ARCH_X64 TRUE PARENT_SCOPE)
-    if(NOT MSVC OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    if(NOT MSVC OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND NOT DISABLE_SSE4)
       set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -msse4.1" PARENT_SCOPE)
       set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -msse4.1" PARENT_SCOPE)
     endif()