Add unsupported calls where needed

A number of tests will exit early without saying why.  This patch adds
"unsupported" at spots like this that I could readily find.

There are definitely more of these; for example dw2-ranges.exp fails
silently because a compilation fails.  I didn't attempt to address
these as that is a much larger task.

gdb/testsuite/gdb.arch/pa-nullify.exp

@@ -26,7 +26,7 @@ switch -glob -- [istarget] {
 	set testfile "pa64-nullify"
     }
     "*" {
-        verbose "Skipping hppa nullification tests."
+        unsupported "Skipping hppa nullification tests."
         return
     }
 }

gdb/testsuite/gdb.arch/powerpc-trap.exp

@@ -29,7 +29,7 @@ if { [istarget powerpc-*] } {
    # with the source file powerpc64-trap.s.
    set expected_traps 5
 } else {
-    verbose "Skipping ${gdb_test_file_name}."
+    unsupported "Skipping powerpc-specific tests"
     return
 }
 

gdb/testsuite/gdb.base/remote.exp

@@ -16,6 +16,7 @@
 # Test only on boards that actually use the remote protocol.
 if {[target_info gdb_protocol] != "remote"
     && [target_info gdb_protocol] != "extended-remote"} {
+    unsupported "requires remote protocol"
     return
 }
 

gdb/testsuite/gdb.base/solib-disc.exp

@@ -19,6 +19,7 @@ require allow_shlib_tests
 
 set gdbserver_reconnect_p 1
 if { [info proc gdb_reconnect] == "" } {
+    unsupported "requires gdbserver reconnect"
     return 0
 }
 

gdb/testsuite/gdb.dwarf2/implptr.exp

@@ -29,6 +29,7 @@ if [info exists COMPILE] {
     lappend opts debug optimize=-O2
 } elseif {![is_x86_like_target]} {
     # This test can only be run on x86 targets.
+    unsupported "needs x86-like target"
     return 0  
 }
 

gdb/testsuite/gdb.server/extended-remote-restart.exp

@@ -30,6 +30,7 @@
 
 # This test is only for extended remote targets.
 if {[target_info gdb_protocol] != "extended-remote"} {
+    unsupported "requires extended-remote"
     return
 }
 
@@ -40,6 +41,7 @@ require {is_any_target "*-*-linux*" "*-*-openbsd*"}
 # And we need to be able to reconnect to gdbserver.
 set gdbserver_reconnect_p 1
 if { [info proc gdb_reconnect] == "" } {
+    unsupported "requires gdbserver reconnect"
     return 0
 }
 

gdb/testsuite/gdb.threads/reconnect-signal.exp

@@ -17,6 +17,7 @@
 
 set gdbserver_reconnect_p 1
 if { [info proc gdb_reconnect] == "" } {
+    unsupported "requires gdbserver reconnect"
     return 0
 }
 

gdb/testsuite/gdb.trace/stap-trace.exp

@@ -115,6 +115,7 @@ if { ![runto_main] } {
 
 if { ![gdb_target_supports_trace] } {
     # Test cannot run on this target.
+    unsupported "test requires trace"
     return 1
 }