[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:
...
gdb_test_multiple <command> <message> {
    -re "\[\r\n\]*(?:<pattern>)\[\r\n\]+$gdb_prompt $" {
    	pass $gdb_test_name
    }
}
...

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

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

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.
	* gdb.reverse/step-precsave.exp: Rewrite gdb_test_multiple containing
	kfail using -cooked pattern flag and convenience variable
	gdb_test_name.

---
 gdb/testsuite/gdb.reverse/step-precsave.exp | 13 +++++--------
 gdb/testsuite/lib/gdb.exp                   | 14 +++++++++++++-
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/gdb/testsuite/gdb.reverse/step-precsave.exp b/gdb/testsuite/gdb.reverse/step-precsave.exp
index 2073b8a1542..3ce786fc4c9 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_name
 	}
-	-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_name
 	}
     }
 }
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index d23d51572cc..f73313f1cb0 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -821,6 +821,7 @@ 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
@@ -835,6 +836,10 @@ 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
@@ -848,7 +853,14 @@ 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 "; "
 	}