AIX: Explicitly compute executable exports for both XL and GNU

On AIX, symbols in executables must be exported in order to be visible
to modules (plugins) they load via `dlopen`.  Prior to policy `CMP0065`,
CMake linked all executables with flags to export symbols, but the NEW
behavior for that policy is to do so only for executables that have the
`ENABLE_EXPORTS` target property set.  In both cases, CMake has always
used the AIX linker option `-bexpall` option to export symbols from
executables.

This has worked fairly well with the XL compiler, but with the GNU
compiler it works only for C ABI symbols.  The reason is that `-bexpall`
does not export symbols starting in `_` but the GNU C++ ABI mangles all
symbols with a leading `_`.  Therefore we have only supported C ABI
plugins with the GNU compiler on AIX.  Some projects have tried to work
around this by replacing `-bexpall` with `-bexpfull`, but the latter
often exports symbols that we do not want exported.

Avoid using `-bexpall` for executables by instead using by our own
internal `ExportImportList` script to compute symbol export lists from
the object files to be linked into an executable.  Pass the explicitly
computed export list to the AIX linker's `-bE:...` option.  We already
do this for shared object exports.

Issue: #19163

2 files changed, 6 insertions, 3 deletions

diff --git a/Tests/RunCMake/CMP0065/RunCMakeTest.cmake b/Tests/RunCMake/CMP0065/RunCMakeTest.cmake
index 254a4ec..e86b50e 100644
--- a/Tests/RunCMake/CMP0065/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CMP0065/RunCMakeTest.cmake
@@ -1,8 +1,11 @@
 include(RunCMake)
 
 run_cmake(OLDBad1)
-run_cmake(OLDBad2)
-run_cmake(NEWBad)
+if(NOT CMAKE_SYSTEM_NAME STREQUAL "AIX")
+  # Tests with ENABLE_EXPORTS ON.  For AIX we do not use the flags at all.
+  run_cmake(OLDBad2)
+  run_cmake(NEWBad)
+endif()
 run_cmake(NEWGood)
 run_cmake(WARN-OFF)
 run_cmake(WARN-ON)
diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 735ad5f..c952b1a 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -120,7 +120,7 @@ add_RunCMake_test(CMP0081)
 # CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS variable, which both the VS and Xcode
 # generators ignore.  The policy will have no effect on those generators.
 if(NOT CMAKE_GENERATOR MATCHES "Visual Studio|Xcode")
-  add_RunCMake_test(CMP0065)
+  add_RunCMake_test(CMP0065 -DCMAKE_SYSTEM_NAME=${CMAKE_SYSTEM_NAME})
 endif()
 if(CMAKE_GENERATOR MATCHES "Make")
   add_RunCMake_test(Make -DMAKE_IS_GNU=${MAKE_IS_GNU})