[PATCH] libstdc++: Work around modules ICE in <charconv> [PR105297]

[Patrick Palka <ppalka@redhat.com>]

This makes the initializer for __table in __from_chars_alnum_to_val
dependent in an artificial way, which works around the modules testsuite
ICE reported in PR105297 by preventing the initializer from getting
evaluated at parse time.

Compared to the alternative workaround of using a non-local class type
for __table, this workaround has the advantage of slightly speeding up
compilation of the <charconv> header, since now the table will not get
built (via constexpr evaluation) until one of the integer std::from_chars
overloads is actually instantiated.

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

	PR c++/105297
	PR c++/105322

libstdc++-v3/ChangeLog:

	* include/std/charconv (__from_chars_alnum_to_val): Make
	initializer for __table dependent in an artificial way.
---
 libstdc++-v3/include/std/charconv | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index f1ace406017..561234cb2fc 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -445,7 +445,9 @@ namespace __detail
 	return __c - '0';
       else
 	{
-	  static constexpr auto __table = __from_chars_alnum_to_val_table();
+	  // This initializer is deliberately made dependent in order to work
+	  // around modules bug PR105322.
+	  static constexpr auto __table = (_DecOnly, __from_chars_alnum_to_val_table());
 	  return __table.__data[__c];
 	}
     }
-- 
2.36.0.rc2.10.g1ac7422e39