Update -zhelp and -chelp rustdoc-ui tests to use regex-error-pattern

src/test/rustdoc-ui/c-help.rs

@@ -1,4 +1,6 @@
 // check-pass
 // compile-flags: -Chelp
+// check-stdout
+// regex-error-pattern: -C\s+incremental
 
 pub struct Foo;

src/test/rustdoc-ui/z-help.rs

@@ -1,4 +1,6 @@
 // check-pass
 // compile-flags: -Zhelp
+// check-stdout
+// regex-error-pattern: -Z\s+self-profile
 
 pub struct Foo;