Unbreak rustc_cg_gcc

Fix lib path.

refs compiler-explorer#5342

Signed-off-by: Marc Poulhiès <dkm@kataplop.net>

lib/compilers/rustc-cg-gcc.ts

@@ -69,7 +69,7 @@ export class RustcCgGCCCompiler extends RustCompiler {
 
         let options = [
             '-Z',
-            'codegen-backend=' + path.join(toolroot, 'librustc_codegen_gcc.so'),
+            'codegen-backend=' + path.join(toolroot, 'lib', 'librustc_codegen_gcc.so'),
             '--sysroot',
             path.join(toolroot, 'sysroot'),
         ];