[libc++] [cmake] Better diagnostics for missing abi library headers

Summary:
This is NFC. We only add additional information to the log.

Reviewers: EricWF, ldionne, mclow.lists

Reviewed By: ldionne

Subscribers: kristof.beyls, dexonsmith, danielkiss, mgorny, ldionne, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D75991

libcxx/cmake/Modules/HandleLibCXXABI.cmake

@@ -37,8 +37,10 @@ macro(setup_abi_lib abidefines abishared abistatic abifiles abidirs)
   foreach(fpath ${LIBCXX_ABILIB_FILES})
     set(found FALSE)
     foreach(incpath ${LIBCXX_CXX_ABI_INCLUDE_PATHS})
+      message(STATUS "Looking for ${fpath} in ${incpath}")
       if (EXISTS "${incpath}/${fpath}")
         set(found TRUE)
+        message(STATUS "Looking for ${fpath} in ${incpath} - found")
         get_filename_component(dstdir ${fpath} PATH)
         get_filename_component(ifile ${fpath} NAME)
         set(src ${incpath}/${fpath})
@@ -66,10 +68,12 @@ macro(setup_abi_lib abidefines abishared abistatic abifiles abidirs)
             PERMISSIONS OWNER_READ OWNER_WRITE GROUP_READ WORLD_READ
             )
         endif()
+      else()
+        message(STATUS "Looking for ${fpath} in ${incpath} - not found")
       endif()
     endforeach()
     if (NOT found)
-      message(WARNING "Failed to find ${fpath}")
+      message(WARNING "Failed to find ${fpath} in ${LIBCXX_CXX_ABI_INCLUDE_PATHS}")
     endif()
   endforeach()