libstdc++: Add comment to 17_intro/names.cc test

libstdc++-v3/ChangeLog:

	* testsuite/17_intro/names.cc: Explain why poison pragma can't
	be used.

diff --git a/libstdc++-v3/testsuite/17_intro/names.cc b/libstdc++-v3/testsuite/17_intro/names.cc
index 86fb8f8999b1c5a5e237b8c8e71d96998397a470..82e201c71b0c7f52a0a3caa36b3538bd9ef4681e 100644 (file)
--- a/libstdc++-v3/testsuite/17_intro/names.cc
+++ b/libstdc++-v3/testsuite/17_intro/names.cc
@@ -20,6 +20,8 @@
 
 // Define macros for some common variables names that we must not use for
 // naming variables, parameters etc. in the library.
+// N.B. we cannot use '#pragma GCC poison A' because that also prevents using
+// these names even as macro arguments, e.g. #define FOO(A) BAR(A)
 #define A (
 #define B (
 #define C (