[libcxx] Respect CMAKE_MSVC_RUNTIME_LIBRARY wrt whether to use the debug CRT

[mstorsjo]

Summary

If CMAKE_MSVC_RUNTIME_LIBRARY isn't set, then CMake defaults to
the debug CRT, if CMAKE_BUILD_TYPE is set to Debug. If
CMAKE_MSVC_RUNTIME_LIBRARY is set though, that overrides any
implicit defaults.

Match this in libcxx's own manual linking logic. This allows
decoupling the debug CRT from the CMAKE_BUILD_TYPE and allows users
to configure their builds exactly how they want.

[andrewng]

LGTM, except for the amount of duplication in these test configs, also mentioned on D155560.

[andrewng]

On the basis that any de-duplication will happen separately.

[Mordante]

I too would like to see less duplication. LGTM!

[mstorsjo]

Rebased

[mstorsjo]

Rebased to place this on top of the deduplication.

[mstorsjo]

Rebase

[mstorsjo]

Rebase

libcxx/CMakeLists.txt

if (LIBCXX_HAS_ATOMIC_LIB)
     target_link_libraries(${target} PRIVATE atomic)
   endif()
 
   if (MINGW)
     target_link_libraries(${target} PRIVATE "${MINGW_LIBRARIES}")
   endif()
 
   if (MSVC)
-    if (uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+    if ((NOT CMAKE_MSVC_RUNTIME_LIBRARY AND uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+        OR (CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "Debug"))
       set(LIB_SUFFIX "d")
     else()
       set(LIB_SUFFIX "")
     endif()
 
     if (NOT CMAKE_MSVC_RUNTIME_LIBRARY OR CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$")
       set(CRT_LIB "msvcrt")
       set(CXX_LIB "msvcprt")

libcxx/test/CMakeLists.txt

if (MSVC)
   if (NOT CMAKE_MSVC_RUNTIME_LIBRARY OR CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$")
     set(crt_lib "msvcrt")
     set(cxx_lib "msvcprt")
   else()
     set(crt_lib "libcmt")
     set(cxx_lib "libcpmt")
   endif()
 
-  if (uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+  if ((NOT CMAKE_MSVC_RUNTIME_LIBRARY AND uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+      OR (CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "Debug"))
     set(dbg_include " -D_DEBUG -include set_windows_crt_report_mode.h")
     set(crt_lib "${crt_lib}d")
     set(cxx_lib "${cxx_lib}d")
   endif()
 
   serialize_lit_param(dbg_include "\"${dbg_include}\"")
   serialize_lit_param(crt_lib "\"${crt_lib}\"")
   serialize_lit_param(cxx_lib "\"${cxx_lib}\"")