[gcc r11-3870] libstdc++: Improve comments for check_effective_target_cxx11-abi

[Jonathan Wakely]

https://gcc.gnu.org/g:a1b6b013615082f0837ea34c5a65136822523be7

commit r11-3870-ga1b6b013615082f0837ea34c5a65136822523be7
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Oct 14 12:09:27 2020 +0100

    libstdc++: Improve comments for check_effective_target_cxx11-abi
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/lib/libstdc++.exp (check_effective_target_cxx11-abi):
            Add comments about which test flags get used by the check.

Diff:
---
 libstdc++-v3/testsuite/lib/libstdc++.exp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp b/libstdc++-v3/testsuite/lib/libstdc++.exp
index 78484f7c9af..fc1e8f242fd 100644
--- a/libstdc++-v3/testsuite/lib/libstdc++.exp
+++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
@@ -1524,6 +1524,8 @@ proc check_v3_target_filesystem_ts { } {
 }
 
 # Return 1 if the "cxx11" ABI is in use using the current flags, 0 otherwise.
+# Any flags provided by RUNTESTFLAGS or a target board will be used here.
+# Flags added in the test by dg-options or dg-add-options will not be used.
 proc check_effective_target_cxx11-abi { } {
     global cxxflags