Rename skip_power_isa_3_1_tests to allow form

This renames skip_power_isa_3_1_tests to allow_power_isa_3_1_tests and
updates its users to use require.

gdb/testsuite/gdb.arch/powerpc-plxv-nonrel.exp

diff --git a/gdb/testsuite/gdb.arch/powerpc-plxv-nonrel.exp b/gdb/testsuite/gdb.arch/powerpc-plxv-nonrel.exp
index a1aacb0..1ad3ea8 100644
--- a/gdb/testsuite/gdb.arch/powerpc-plxv-nonrel.exp
+++ b/gdb/testsuite/gdb.arch/powerpc-plxv-nonrel.exp
@@ -16,10 +16,11 @@
 # Test to see if gdb is properly single stepping over the
 # displaced plxv instruction.
 
-if { ![istarget powerpc*-*] || [skip_power_isa_3_1_tests] } {
+if { ![istarget powerpc*-*] } {
     verbose "Skipping powerpc ISA 3.1 plxv test."
     return
 }
+require allow_power_isa_3_1_tests
 
 set retval 0
 

gdb/testsuite/gdb.reverse/ppc_record_test_isa_3_1.exp

diff --git a/gdb/testsuite/gdb.reverse/ppc_record_test_isa_3_1.exp b/gdb/testsuite/gdb.reverse/ppc_record_test_isa_3_1.exp
index f6bf485..7a291aa 100644
--- a/gdb/testsuite/gdb.reverse/ppc_record_test_isa_3_1.exp
+++ b/gdb/testsuite/gdb.reverse/ppc_record_test_isa_3_1.exp
@@ -37,10 +37,11 @@
 set gen_src record_test_isa_3_1.c
 set executable record_test_isa_3_1
 
-if {![istarget "powerpc*"] || [skip_power_isa_3_1_tests]}  {
+if {![istarget "powerpc*"]}  {
     verbose "Skipping PowerPC ISA 3.1 instruction record_test."
     return
 }
+require allow_power_isa_3_1_tests
 
 set options [list additional_flags=-mcpu=power10 debug]
 if {[build_executable "failed to prepare" $executable $srcfile $options] == -1} {

gdb/testsuite/lib/gdb.exp

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 2c53ebe..5425ae7 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -3525,10 +3525,10 @@
 }
 
 # Run a test on the power target to see if it supports ISA 3.1 instructions
-gdb_caching_proc skip_power_isa_3_1_tests {
+gdb_caching_proc allow_power_isa_3_1_tests {
     global srcdir subdir gdb_prompt inferior_exited_re
 
-    set me "skip_power_isa_3_1_tests"
+    set me "allow_power_isa_3_1_tests"
 
     # Compile a test program containing ISA 3.1 instructions.
     set src {
@@ -3540,7 +3540,7 @@
 	}
 
     if {![gdb_simple_compile $me $src executable ]} {
-        return 1
+	return 0
     }
 
     # No error message, compilation succeeded so now run it via gdb.
@@ -3553,22 +3553,22 @@
     gdb_expect {
         -re ".*Illegal instruction.*${gdb_prompt} $" {
             verbose -log "\n$me Power ISA 3.1 hardware not detected"
-            set skip_power_isa_3_1_tests 1
+	    set allow_power_isa_3_1_tests 0
         }
         -re ".*$inferior_exited_re normally.*${gdb_prompt} $" {
             verbose -log "\n$me: Power ISA 3.1 hardware detected"
-            set skip_power_isa_3_1_tests 0
+	    set allow_power_isa_3_1_tests 1
         }
         default {
-          warning "\n$me: default case taken"
-            set skip_power_isa_3_1_tests 1
+	    warning "\n$me: default case taken"
+	    set allow_power_isa_3_1_tests 0
         }
     }
     gdb_exit
     remote_file build delete $obj
 
-    verbose "$me:  returning $skip_power_isa_3_1_tests" 2
-    return $skip_power_isa_3_1_tests
+    verbose "$me:  returning $allow_power_isa_3_1_tests" 2
+    return $allow_power_isa_3_1_tests
 }
 
 # Run a test on the target to see if it supports vmx hardware.  Return 0 if so,