[PATCH,testsuite] Add check_effective_target_rdynamic and use it in g++.dg/lto/pr69589_0.C.

[Toma Tabacu <Toma dot Tabacu at imgtec dot com>]

Hi,

g++.dg/lto/pr69589_0.C is currently failing for mips-mti-elf with the following error:

xg++: error: unrecognized command line option '-rdynamic'

However, it passes just fine for mips-mti-linux-gnu.
I think that we should skip this test for mips-mti-elf.

This patch achieves this by adding support for check_effective_target_rdynamic
and then using it in g++.dg/lto/pr69589_0.C.

This patch also removes the existing dg-skip-if, as it is made redundant by the
effective target check. The latter is also more convenient, as we won't have to
keep tweaking the dg-skip-if for failing targets anymore.

This is similar to my recent check_effective_target_gettimeofday patch,
which was greatly improved by Rainer Orth's review.

Tested with mips-mti-elf and mips-mti-linux-gnu.

Does this look good ?

Regards,
Toma

gcc/
	* doc/sourcebuild.texi (Effective-Target Keywords, Other attributes):
	Document rdynamic.

gcc/testsuite/

	* g++.dg/lto/pr69589_0.C: Add dg-require-effective-target for
	rdynamic.  Remove dg-skip-if for targets which don't support -rdynamic.
	* lib/target-supports.exp (check_effective_target_rdynamic):
	New proc.

diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 0dc4348..d75e078 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2065,6 +2065,9 @@ Target supports @option{-mpe-aligned-commons}.
 @item pie
 Target supports @option{-pie}, @option{-fpie} and @option{-fPIE}.
 
+@item rdynamic
+Target supports @option{-rdynamic}.
+
 @item section_anchors
 Target supports section anchors.
 
diff --git a/gcc/testsuite/g++.dg/lto/pr69589_0.C b/gcc/testsuite/g++.dg/lto/pr69589_0.C
index 11766f1..599d5d4 100644
--- a/gcc/testsuite/g++.dg/lto/pr69589_0.C
+++ b/gcc/testsuite/g++.dg/lto/pr69589_0.C
@@ -1,7 +1,7 @@
 // { dg-lto-do link }
 // { dg-lto-options "-O2 -rdynamic" }
 // { dg-extra-ld-options "-r -nostdlib" }
-// { dg-skip-if "Skip targets without -rdynamic support" { arm*-none-eabi aarch64*-*-elf nios2-*-elf } { "*" } { "" } }
+// { dg-require-effective-target rdynamic }
 
 #pragma GCC visibility push(hidden)
 struct A { int &operator[] (long); };
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 2766af4..f46f0ba 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -1484,6 +1484,16 @@ proc check_effective_target_static_libgfortran { } {
     } "-static"]
 }
 
+# Return 1 if we can use the -rdynamic option, 0 otherwise.
+#
+# When the target name changes, replace the cached result.
+
+proc check_effective_target_rdynamic { } {
+  return [check_no_compiler_messages rdynamic executable {
+     int main() { return 0; }
+  } "-rdynamic"]
+}
+
 # Return 1 if cilk-plus is supported by the target, 0 otherwise.
  
 proc check_effective_target_cilkplus { } {