Fix some compiler warnings seen in Buildbot.

Add some extra error output and code cleanup in an attempt to fix/debug
a rare random testsuite problem in check_warnings, where the exit code
from mysqltest is somehow corrupted inside mysql-test-run.pl.

include/my_global.h:
  Fix compiler warnings on some platforms.
mysql-test/lib/My/SafeProcess.pm:
  Move dereference of $? subprocess exit code closer to where it is generated,
  to make the code more robust and on the chance that this will fix the
  occasional problems in check_warnings we see in Buildbot.
mysql-test/mysql-test-run.pl:
  When check_warnings failed, also log the mysqld server for which it failed.
sql/sql_lex.cc:
  Fix compiler warning about possibly uninitialised value, by rewriting a for()
  loop that is always executed at least once into a do .. while() loop with an
  assert.
sql/table.cc:
  Fix compiler warning about uninitialised value.
storage/federatedx/ha_federatedx.cc:
  Fix uninitialised variable.
storage/maria/ma_delete.c:
  Fix compiler warning about uninitialised value.
storage/maria/ma_loghandler.c:
  Fix compiler warning about uninitialised value.
storage/myisam/ft_stopwords.c:
  Fix compiler warning.
storage/myisam/mi_write.c:
  Fix compiler warning about possibly uninitialised value, by rewriting a while()
  loop that is always executed at least once into a do .. while() loop with an
  assert.
storage/xtradb/btr/btr0cur.c:
  Fix compiler warning about possibly uninitialised value.
support-files/compiler_warnings.supp:
  Fix warning suppression to cover all cases in yassl.
vio/viossl.c:
  Fix compiler warning.

mysql-test/lib/My/SafeProcess.pm

@@ -384,9 +384,9 @@ sub kill {
 
 
 sub _collect {
-  my ($self)= @_;
+  my ($self, $exit_code)= @_;
 
-  $self->{EXIT_STATUS}= $?;
+  $self->{EXIT_STATUS}= $exit_code;
   _verbose("_collect: $self");
 
   # Take the process out of running list
@@ -453,6 +453,7 @@ sub wait_one {
   #_verbose("blocking: $blocking, use_alarm: $use_alarm");
 
   my $retpid;
+  my $exit_code;
   eval
   {
     # alarm should break the wait
@@ -461,6 +462,7 @@ sub wait_one {
     alarm($timeout) if $use_alarm;
 
     $retpid= waitpid($pid, $blocking ? 0 : &WNOHANG);
+    $exit_code= $?;
 
     alarm(0) if $use_alarm;
   };
@@ -492,7 +494,7 @@ sub wait_one {
   #warn "wait_one: expected pid $pid but got $retpid"
   #  unless( $retpid == $pid );
 
-  $self->_collect();
+  $self->_collect($exit_code);
   return 0;
 }
 
@@ -505,6 +507,8 @@ sub wait_one {
 #
 sub wait_any {
   my $ret_pid;
+  my $exit_code;
+
   if (IS_WIN32PERL) {
     # Can't wait for -1 => use a polling loop
     do {
@@ -514,6 +518,7 @@ sub wait_any {
 	last if $pid == $ret_pid;
       }
     } while ($ret_pid == 0);
+    $exit_code= $?;
   }
   else
   {
@@ -523,6 +528,7 @@ sub wait_any {
       print STDERR "wait_any, got invalid pid: $ret_pid\n";
       return undef;
     }
+    $exit_code= $?;
   }
 
   # Look it up in "running" table
@@ -532,7 +538,7 @@ sub wait_any {
     print STDERR "running: ". join(", ", keys(%running)). "\n";
     return undef;
   }
-  $proc->_collect;
+  $proc->_collect($exit_code);
   return $proc;
 }