make pointer regular expressions more flexible

We just got a failure on Mac on CI with pointers past eight digits:

    (0x10432dec0,0x10433c690)

Use `[[:xdigit:]]+` consistently.

testdata/script/reverse.txtar

@@ -102,7 +102,7 @@ func printStackTrace(w io.Writer) error {
 	// The format also changes depending on the ABI.
 	// Strip them out here, to have portable static stdout files.
 	rxCallArgs := regexp.MustCompile(`\(({|0x)[^)]+\)|\(\)`)
-	rxPointer := regexp.MustCompile(`\+0x[0-9a-f]+`)
+	rxPointer := regexp.MustCompile(`\+0x[[:xdigit:]]+`)
 
 	// Keep this comment here, because comments affect line numbers.
 

testdata/script/tiny.txtar

@@ -4,7 +4,7 @@ exec garble -tiny build
 env GODEBUG='allocfreetrace=1,gcpacertrace=1,gctrace=1,inittrace=1,scavenge=1,scavtrace=1,scheddetail=1,schedtrace=10'
 ! exec ./main$exe
 env GODEBUG='' # Ensure further commands don't have weirdness due to GODEBUG.
-stderr '^\(0x[\d\w]{4,8},0x[\d\w]{4,8}\)' # interfaces/pointers print correctly
+stderr '^\(0x[[:xdigit:]]+,0x[[:xdigit:]]+\)' # interfaces/pointers print correctly
 # With -tiny, all line numbers are reset to 1.
 # Unfortunately, line comment directives don't allow erasing line numbers entirely.
 stderr '^caller: \?\? 1$' # position info is removed
@@ -19,7 +19,7 @@ stderr 'funcStructExported false funcStructUnexported true'
 # Default mode
 exec garble build
 ! exec ./main$exe
-stderr '^caller: [0-9a-zA-Z_]+\.go [1-9]'
+stderr '^caller: [[:word:]]+\.go [1-9]'
 stderr '^recovered: ya like jazz?'
 stderr 'panic: oh noes'
 stderr 'funcExported false funcUnexported false'