[PATCH] AIX visibility

[David Edelsohn <dje dot gcc at gmail dot com>]

This patch enables visibility support for AIX.  AIX of course chose
different syntax, so the default machinery isn't usable.  AIX appends
the visibility to the .globl and .comm pseudo-ops.

Within the rs6000 port, this patch only affects AIX / XCOFF.

Also, because visibility support implicitly enables other features in
GCC, some of which conflict with AIX, I had to disable the additional
features.  Because AIX uses DWARF for EH but places the DWARF
information in the data section, the use of DWARF references and
force_constant_mem conflicts with the data section.  For this reason,
USE_LINKONCE_INDIRECT is disabled in dwarf2asm.c.

This patch also adjusts gcc/configure to set HAVE_GAS_HIDDEN. AIX ld
support for hidden is forced true because the assembler test will
catch if support is present.

A number of testsuite tweaks also are necessary to XFAIL some
visibility tests on AIX.

Bootstrapped on powerpc-ibm-aix7.2.0.0 and powerpc64le-ibm-linux-gnu.

Are the changes to configure and dwarf2asm.c okay?

* configure.ac (.hidden): Change to conftest_s string. Provide string
for AIX assembler.
(gcc_cv_ld_hidden): Yes for AIX.
* configure: Regenerate.

* dwarf2asm.c (USE_LINKONCE_INDIRECT): Don't set for AIX (XCOFF).

* config/rs6000/rs6000-protos.h
(rs6000_xcoff_asm_output_aligned_decl_common): Declare.
* config/rs6000/xcoff.h (TARGET_ASM_GLOBALIZE_DECL_NAME): Define.
(ASM_OUTPUT_ALIGNED_DECL_COMMON): Define.
(ASM_OUTPUT_ALIGNED_COMMON): Delete.
* config/rs6000/rs6000.c (rs6000_xcoff_visibility): New.
(rs6000_xcoff_declare_function_name): Add visibility support.
(rs6000_xcoff_asm_globalize_decl_name): New.
(rs6000_xcoff_asm_output_aligned_decl_common): New.
(rs6000_code_end): Disable HIDDEN_LINKONCE on XCOFF.

Thanks, David

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