[SystemZ][ZOS] Prefer -nostdlib++ as opposed to -nodefaultlibs when building c++ libraries
Let's use -nostdlib++ rather than -nodefaultlibs when building libc++/libc++abi/libunwind libraries. The default is -nostdlib++ if supported by a build compiler like it is the case with clang, otherwise -nodefaultlibs is used as before.
This change is needed to avoid additional changes at the link step and not to increase the maintenance costs. If clang with -nodefaultlibs is used all the libraries which are removed but required would have to be manually added in. This set of libraries are unique and will send out.
The propose change will allow to make the link step simple for other platforms as well.
Reviewed By: #libc, #libc_abi, ldionne
Differential Revision: https://reviews.llvm.org/D95875
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 43f7cbb..1144f45 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -725,9 +725,19 @@
# Link system libraries =======================================================
function(cxx_link_system_libraries target)
- target_add_link_flags_if_supported(${target} PRIVATE "-nodefaultlibs")
- target_add_compile_flags_if_supported(${target} PRIVATE "/Zl")
- target_add_link_flags_if_supported(${target} PRIVATE "/nodefaultlib")
+
+# In order to remove just libc++ from the link step
+# we need to use -nostdlib++ whenever it is supported.
+# Unfortunately this cannot be used universally because for example g++ supports
+# only -nodefaultlibs in which case all libraries will be removed and
+# all libraries but c++ have to be added in manually.
+ if (LIBCXX_SUPPORTS_NOSTDLIBXX_FLAG)
+ target_add_link_flags_if_supported(${target} PRIVATE "-nostdlib++")
+ else()
+ target_add_link_flags_if_supported(${target} PRIVATE "-nodefaultlibs")
+ target_add_compile_flags_if_supported(${target} PRIVATE "/Zl")
+ target_add_link_flags_if_supported(${target} PRIVATE "/nodefaultlib")
+ endif()
if (LIBCXX_HAS_SYSTEM_LIB)
target_link_libraries(${target} PRIVATE System)
