gdb.base/examine-backward.exp C++ify and Clang

Adjust gdb.base/examine-backward.exp to let the testcase build and run
as a C++ program, built with either G++ or Clang++.

The change to use unsigned char instead of plain char is to avoid
narrowing warnings:

  gdb compile failed, src/gdb/testsuite/gdb.base/examine-backward.c:55:1: error: narrowing conversion of '227' from 'int' to 'char' [-Wnarrowing]
     55 | };
	| ^

gdb/testsuite/ChangeLog:

	* gdb.base/examine-backward.c (Barrier, TestStrings): Now unsigned
	char array.
	(main): Add references to Barrier, TestStrings, TestStringsH and
	TestStringsW.
	* gdb.base/examine-backward.exp: Issue "set print asm-demangle on"
	and expect a full prototype in C++.

1 files changed, 5 insertions, 2 deletions

diff --git a/gdb/testsuite/gdb.base/examine-backward.exp b/gdb/testsuite/gdb.base/examine-backward.exp
index c1ab4d1ce8d..b2d9fc1e1b2 100644
--- a/gdb/testsuite/gdb.base/examine-backward.exp
+++ b/gdb/testsuite/gdb.base/examine-backward.exp
@@ -345,9 +345,12 @@ with_test_prefix "backward disassemble general" {
     set length_to_examine {1 2 3 4 10}
     set disassmbly {}
 
-    gdb_test "x/i main" "0x\[0-9a-fA-F\]+ <main>:\t.*" \
+    gdb_test_no_output "set print asm-demangle on"
+    set main_re "main(\\(\\))?"
+
+    gdb_test "x/i main" "0x\[0-9a-fA-F\]+ <$main_re>:\t.*" \
         "move the current position to main (x/i)"
-    gdb_test "x/-i" "0x\[0-9a-fA-F\]+ <main>:\t.*" \
+    gdb_test "x/-i" "0x\[0-9a-fA-F\]+ <$main_re>:\t.*" \
         "move the current position to main (x/-i)"
     for {set i 0} {$i < [llength $length_to_examine]} {incr i} {
         set len [lindex $length_to_examine $i]