[gdb/testsuite] Add -cooked pattern flag to gdb_test_multiple

Currently, in order to rewrite:
...
gdb_test <command> <pattern> <message>
...
using gdb_test_multiple, we get:
...
set msg <message>
gdb_test_multiple <command> $msg {
    -re "\[\r\n\]*(?:<pattern>)\[\r\n\]+$gdb_prompt $" {
    	pass $msg
    }
}
...

Add to gdb_test_multiple:
- a '-cooked' pattern flag, that wraps the regexp pattern as gdb_test wraps
  its message argument.
- a convenience variable gdb_test_multiple_message

This allows us to rewrite into the more compact:
...
gdb_test_multiple <command> <message> {
    -re -cooked <pattern> {
        pass $gdb_test_multiple_message
    }
}
...

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2019-10-04  Tom de Vries  <tdevries@suse.de>

	* lib/gdb.exp (gdb_test_multiple): Add -cooked pattern flag and
	convenience variable gdb_test_multiple_message.
	* gdb.reverse/step-precsave.exp: Rewrite gdb_test_multiple containing
	kfail using -cooked pattern flag and convenience variable
	gdb_test_multiple_message.

---
 gdb/testsuite/gdb.reverse/step-precsave.exp | 13 +++++--------
 gdb/testsuite/lib/gdb.exp                   | 25 ++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 9 deletions(-)

diff --git a/gdb/testsuite/gdb.reverse/step-precsave.exp b/gdb/testsuite/gdb.reverse/step-precsave.exp
index 2073b8a1542..aaddd3b4ada 100644
--- a/gdb/testsuite/gdb.reverse/step-precsave.exp
+++ b/gdb/testsuite/gdb.reverse/step-precsave.exp
@@ -46,15 +46,12 @@ gdb_test "break $end_of_main" \
 
 # This can take awhile.
 with_timeout_factor 20 {
-    set test "run to end of main"
-    set pass_pattern "Breakpoint .* end of main .*"
-    set kfail_pattern "Process record does not support instruction 0xc5 at.*"
-    gdb_test_multiple "continue" $test {
-	-re "\[\r\n\]*(?:$pass_pattern)\[\r\n\]+$gdb_prompt $" {
-	    pass $test
+    gdb_test_multiple "continue" "run to end of main" {
+	-re -cooked "Breakpoint .* end of main .*" {
+	    pass $gdb_test_multiple_message
 	}
-	-re "\[\r\n\]*(?:$kfail_pattern)\[\r\n\]+$gdb_prompt $" {
-	    kfail "record/23188" $test
+	-re -cooked "Process record does not support instruction 0xc5 at.*" {
+	    kfail "record/23188" $gdb_test_multiple_message
 	}
     }
 }
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 3a1f053cf8a..4a47ddc9d37 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -772,6 +772,11 @@ proc gdb_test_multiple { command message user_code { prompt_regexp "" } } {
 	error "Invalid newline in \"$message\" test"
     }
 
+    upvar 1 gdb_test_multiple_message gdb_test_multiple_message
+    if { [info exists gdb_test_multiple_message] } {
+	set gdb_test_multiple_message_save $gdb_test_multiple_message
+    }
+
     if {$use_gdb_stub
 	&& [regexp -nocase {^\s*(r|run|star|start|at|att|atta|attac|attach)\M} \
 	    $command]} {
@@ -807,6 +812,7 @@ proc gdb_test_multiple { command message user_code { prompt_regexp "" } } {
     set patterns ""
     set expecting_action 0
     set expecting_arg 0
+    set cooked 0
     foreach item $user_code subst_item $subst_code {
 	if { $item == "-n" || $item == "-notransfer" || $item == "-nocase" } {
 	    lappend processed_code $item
@@ -821,6 +827,10 @@ proc gdb_test_multiple { command message user_code { prompt_regexp "" } } {
 	    lappend processed_code $item
 	    continue
 	}
+	if { $item == "-cooked" } {
+	    set cooked 1
+	    continue
+	}
 	if { $expecting_arg } {
 	    set expecting_arg 0
 	    lappend processed_code $subst_item
@@ -834,7 +844,14 @@ proc gdb_test_multiple { command message user_code { prompt_regexp "" } } {
 	    continue
 	}
 	set expecting_action 1
-	lappend processed_code $subst_item
+	if { $cooked } {
+	    # Wrap subst_item as is done for the gdb_test PATTERN argument.
+	    lappend processed_code \
+		"\[\r\n\]*(?:$subst_item)\[\r\n\]+$gdb_prompt $"
+	    set cooked 0
+	} else {
+	    lappend processed_code $subst_item
+	}
 	if {$patterns != ""} {
 	    append patterns "; "
 	}
@@ -1038,8 +1055,14 @@ proc gdb_test_multiple { command message user_code { prompt_regexp "" } } {
 	}
     }
 
+    set gdb_test_multiple_message $message
     set result 0
     set code [catch {gdb_expect $code} string]
+    if { [info exists gdb_test_multiple_message_save] } {
+	set gdb_test_multiple_message $gdb_test_multiple_message_save
+    } else {
+	unset gdb_test_multiple_message
+    }
     if {$code == 1} {
 	global errorInfo errorCode
 	return -code error -errorinfo $errorInfo -errorcode $errorCode $string