[libcxx] Consistently set CMAKE_STATIC_LIBRARY_PREFIX regardless of LIBCXX_ENABLE_STATIC

[mstorsjo]

Summary

CMAKE_STATIC_LIBRARY_PREFIX affects the naming of all static libs (in
MSVC configurations), including c++experimental, which only is produced
as static regardless of LIBCXX_ENABLE_STATIC.

[curdeius]

LGTM.

[ldionne]

I think even better would be to get rid of the need to compute the name of the static library, but this is still a slight improvement.

[mstorsjo]

In D99176#2644866, @ldionne wrote:

I think even better would be to get rid of the need to compute the name of the static library, but this is still a slight improvement.

Yup, but even then, this one makes sure that we are consistent in setting our preference for how cmake names things.

libcxx/src/CMakeLists.txt

if(WIN32 AND NOT MINGW AND NOT "${CMAKE_HOST_SYSTEM_NAME}" STREQUAL "Windows")
     # Since we most likely do not have a mt.exe replacement, disable the
     # manifest bundling.  This allows a normal cmake invocation to pass which
     # will attempt to use the manifest tool to generate the bundled manifest
     set_target_properties(cxx_shared PROPERTIES
                           APPEND_STRING PROPERTY LINK_FLAGS " /MANIFEST:NO")
   endif()
 endif()
 
+set(CMAKE_STATIC_LIBRARY_PREFIX "lib")
+
 # Build the static library.
 if (LIBCXX_ENABLE_STATIC)
   add_library(cxx_static STATIC ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
   target_link_libraries(cxx_static PUBLIC cxx-headers
                                    PRIVATE ${LIBCXX_LIBRARIES})
-  set(CMAKE_STATIC_LIBRARY_PREFIX "lib")
   set_target_properties(cxx_static
     PROPERTIES
       COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
       LINK_FLAGS    "${LIBCXX_LINK_FLAGS}"
       OUTPUT_NAME   "c++"
   )
   cxx_add_common_build_flags(cxx_static)
   cxx_set_common_defines(cxx_static)