[gdb/testsuite] Disable inferior output in gdb.base/foll-vfork.exp

Test-case gdb.base/foll-vfork.exp has inferior output that is not needed, but
which makes the regexp matching more difficult (see commit 1f28b70def1
"[gdb/testsuite] Fix regexp in gdb.base/foll-vfork.exp").

Disable the inferior output using '#if DEBUG'.

Tested on x86_64-linux.

---
 gdb/testsuite/gdb.base/foll-vfork-exit.c | 14 ++++++++++++--
 gdb/testsuite/gdb.base/foll-vfork.c      |  9 ++++++++-
 gdb/testsuite/gdb.base/foll-vfork.exp    | 17 +++++++++++------
 gdb/testsuite/gdb.base/vforked-prog.c    |  7 ++++++-
 4 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/gdb/testsuite/gdb.base/foll-vfork-exit.c b/gdb/testsuite/gdb.base/foll-vfork-exit.c
index 6c263cdc057..15e272afe82 100644
--- a/gdb/testsuite/gdb.base/foll-vfork-exit.c
+++ b/gdb/testsuite/gdb.base/foll-vfork-exit.c
@@ -29,12 +29,22 @@ main ()
   pid = vfork (); /* VFORK */
   if (pid == 0)
     {
-      printf ("I'm the child!\n");
+      const char *s = "I'm the child!";
+#if DEBUG
+      printf ("%s\n", s);
+#else
+    const char *volatile v = s;
+#endif
       _exit (0);
     }
   else
     {
-      printf ("I'm the proud parent of child #%d!\n", pid);
+      const char *s = "I'm the proud parent of child";
+#if DEBUG
+      printf ("%s #%d!\n", s, pid);
+#else
+    const char *volatile v = s;
+#endif
     }
 
   return 0;
diff --git a/gdb/testsuite/gdb.base/foll-vfork.c b/gdb/testsuite/gdb.base/foll-vfork.c
index 2f6661d1a0b..b7e332e146b 100644
--- a/gdb/testsuite/gdb.base/foll-vfork.c
+++ b/gdb/testsuite/gdb.base/foll-vfork.c
@@ -40,12 +40,19 @@ main (int argc, char ** argv)
     memcpy (prog + len - 10, "vforked-prog", 12);
     prog[len + 2] = 0;
 
+#if DEBUG
     printf ("I'm the child!\n");
+#endif
     execlp (prog, prog, (char *) 0);
     perror ("exec failed");
     _exit (1);
   }
   else {
-    printf ("I'm the proud parent of child #%d!\n", pid);
+    const char *s = "I'm the proud parent of child";
+#if DEBUG
+    printf ("%s #%d!\n", s, pid);
+#else
+    const char *volatile v = s;
+#endif
   }
 }
diff --git a/gdb/testsuite/gdb.base/foll-vfork.exp b/gdb/testsuite/gdb.base/foll-vfork.exp
index a781a5c2087..fc710167f7d 100644
--- a/gdb/testsuite/gdb.base/foll-vfork.exp
+++ b/gdb/testsuite/gdb.base/foll-vfork.exp
@@ -32,9 +32,14 @@ if [gdb_debug_enabled] {
     return 0
 }
 
+# Set DEBUG to 0 or 1 in sources.
+set debug 0
+
 standard_testfile
 
-set compile_options debug
+set compile_options {}
+lappend compile_options debug
+lappend compile_options additional_flags=-DDEBUG=$debug
 
 if {[build_executable $testfile.exp $testfile $srcfile $compile_options] == -1} {
     untested "failed to compile main testcase"
@@ -126,7 +131,7 @@ proc vfork_parent_follow_to_bp {} {
 
    gdb_test_no_output "set follow-fork parent"
 
-   set bp_location [gdb_get_line_number "printf (\"I'm the proud parent of child"]
+   set bp_location [gdb_get_line_number "I'm the proud parent of child"]
    gdb_test "break ${srcfile}:${bp_location}" ".*" "break, vfork to bp"
 
    set test "continue to bp"
@@ -176,7 +181,7 @@ proc vfork_and_exec_child_follow_to_main_bp {} {
 
    gdb_test_no_output "set follow-fork child"
 
-   set linenum [gdb_get_line_number "printf(\"Hello from vforked-prog" ${srcfile2}]
+   set linenum [gdb_get_line_number "Hello from vforked-prog" ${srcfile2}]
 
    set test "continue to bp"
    gdb_test_multiple "continue" $test {
@@ -278,7 +283,7 @@ proc tcatch_vfork_then_child_follow_exec {} {
    continue_to_vfork
 
    set linenum1 [gdb_get_line_number "pid = vfork ();"]
-   set linenum2 [gdb_get_line_number "printf(\"Hello from vforked-prog" ${srcfile2}]
+   set linenum2 [gdb_get_line_number "Hello from vforked-prog" ${srcfile2}]
 
    set test "finish"
    gdb_test_multiple "finish" $test {
@@ -356,7 +361,7 @@ proc vfork_relations_in_info_inferiors { variant } {
    if { $variant == "exec" } {
        global srcfile2
 
-       set linenum [gdb_get_line_number "printf(\"Hello from vforked-prog" ${srcfile2}]
+       set linenum [gdb_get_line_number "Hello from vforked-prog" ${srcfile2}]
        set test "continue to bp"
        gdb_test_multiple "continue" $test {
 	   -re ".*xecuting new program.*Breakpoint.*vforked-prog.c:${linenum}.*$gdb_prompt " {
@@ -487,7 +492,7 @@ set testfile "foll-vfork-exit"
 set srcfile ${testfile}.c
 set binfile [standard_output_file ${testfile}]
 
-if {[build_executable $testfile.exp $testfile $srcfile] == -1} {
+if {[build_executable $testfile.exp $testfile $srcfile $compile_options] == -1} {
     untested "failed to build $testfile"
     return
 }
diff --git a/gdb/testsuite/gdb.base/vforked-prog.c b/gdb/testsuite/gdb.base/vforked-prog.c
index 936c6e6032d..999efa8ce0d 100644
--- a/gdb/testsuite/gdb.base/vforked-prog.c
+++ b/gdb/testsuite/gdb.base/vforked-prog.c
@@ -19,6 +19,11 @@
 
 int main (void)
 {
-  printf("Hello from vforked-prog...\n");
+  const char *s = "Hello from vforked-prog";
+#if DEBUG
+  printf ("%s...\n", s);
+#else
+  const char *volatile v = s;
+#endif
   return 0;
 }