ada: Introduce -gnateH switch to force reverse Bit_Order threshold to 64

This can be helpful for legacy code that still makes use of an original
reverse Bit_Order clause, i.e. without a Scalar_Storage_Order clause.

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst (Compiler
	Switches): Document -gnateH.
	* opt.ads (Reverse_Bit_Order_Threshold): New variable.
	* sem_ch13.adb (Adjust_Record_For_Reverse_Bit_Order): Use its value
	if it is nonnegative instead of System_Max_Integer_Size.
	* switch-c.adb (Scan_Front_End_Switches): Deal with -gnateH.
	* usage.adb (Usage): Print -gnateH.
	* gnat_ugn.texi: Regenerate.

1 files changed, 13 insertions, 1 deletions

diff --git a/gcc/ada/gnat_ugn.texi b/gcc/ada/gnat_ugn.texi
index 88123df..021c267 100644
--- a/gcc/ada/gnat_ugn.texi
+++ b/gcc/ada/gnat_ugn.texi
@@ -19,7 +19,7 @@
 
 @copying
 @quotation
-GNAT User's Guide for Native Platforms , Jun 01, 2023
+GNAT User's Guide for Native Platforms , Jun 16, 2023
 
 AdaCore
 
@@ -9075,6 +9075,18 @@ information.
 Save result of preprocessing in a text file.
 @end table
 
+@geindex -gnateH (gcc)
+
+
+@table @asis
+
+@item @code{-gnateH}
+
+Set the threshold from which the RM 13.5.1(13.3/2) clause applies to 64.
+This is useful only on 64-bit plaforms where this threshold is 128, but
+used to be 64 in earlier versions of the compiler.
+@end table
+
 @geindex -gnatei (gcc)