remap-path-prefix-sysroot: remap {{src-base}} as well

This is done to cover the path of the test it-self as it may not live
on the same root directory as {{rust-src-base}}, which can be the case
if {{rust-src-base}} is coming from a extracted dist build (cc opt-dist)

tests/ui/errors/remap-path-prefix-sysroot.rs

@@ -1,6 +1,7 @@
 //@ revisions: with-remap without-remap
 //@ compile-flags: -g -Ztranslate-remapped-path-to-local-path=yes
 //@ [with-remap]compile-flags: --remap-path-prefix={{rust-src-base}}=remapped
+//@ [with-remap]compile-flags: --remap-path-prefix={{src-base}}=remapped-tests-ui
 //@ [without-remap]compile-flags:
 //@ error-pattern: E0507
 

tests/ui/errors/remap-path-prefix-sysroot.with-remap.stderr

@@ -1,5 +1,5 @@
 error[E0507]: cannot move out of `self.thread` which is behind a mutable reference
-  --> remapped/tests/ui/errors/remap-path-prefix-sysroot.rs:LL:COL
+  --> remapped-tests-ui/errors/remap-path-prefix-sysroot.rs:LL:COL
    |
 LL |         self.thread.join().unwrap();
    |         ^^^^^^^^^^^ ------ `self.thread` moved due to this method call