[libcxx] Fix the definition of the check-cxx-abilist target on Darwin

[ldionne]

Summary

r342805 added support for the check-cxx-abilist target on FreeBSD, but broke
the target on macOS in doing so. The problem is that the GENERIC_TARGET_TRIPLE
gets overwritten after replacing the FreeBSD regular expression, which
nullifies the replacement done with the darwin regular expression.

[ldionne]

Remove the change to the Darwin ABI list file, which was meant for a different commit.

[dim]

Ah, sorry about that! I should have realized this, but my CMake-fu is weak. :)

libcxx/lib/abi/CMakeLists.txt

 
 if (DEFINED TARGET_TRIPLE)
+    if (TARGET_TRIPLE MATCHES "darwin")
         # Ignore the major, minor, and patchlevel versions of darwin targets.
         string(REGEX REPLACE "darwin[0-9]+\\.[0-9]+\\.[0-9]+" "darwin"
                GENERIC_TARGET_TRIPLE "${TARGET_TRIPLE}")
-
+    elseif(TARGET_TRIPLE MATCHES "freebsd")
         # Ignore the major and minor versions of freebsd targets.
         string(REGEX REPLACE "freebsd[0-9]+\\.[0-9]+" "freebsd"
                GENERIC_TARGET_TRIPLE "${TARGET_TRIPLE}")
+    else()
+        set(GENERIC_TARGET_TRIPLE "${TARGET_TRIPLE}")
+    endif()
 endif()
 
 # Detect if we are building in the same configuration used to generate
 # the abilist files.
 set(ABILIST_FILE "${CMAKE_CURRENT_LIST_DIR}/${GENERIC_TARGET_TRIPLE}.v${LIBCXX_ABI_VERSION}.abilist")
 set(SYMDIFF_EXE "${LIBCXX_SOURCE_DIR}/utils/sym_diff.py")
 if (EXISTS "${ABILIST_FILE}"
     AND TARGET cxx_shared