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

1 files changed, 3 insertions, 0 deletions

diff --git a/Source/cmTarget.h b/Source/cmTarget.h
index d9e87b8..a808bb4 100644
--- a/Source/cmTarget.h
+++ b/Source/cmTarget.h
@@ -180,6 +180,9 @@ public:
   //! Return whether or not the target is for a DLL platform.
   bool IsDLLPlatform() const;
 
+  //! Return whether or not we are targeting AIX.
+  bool IsAIX() const;
+
   bool IsImported() const;
   bool IsImportedGloballyVisible() const;