gccrs: Adds and fixes tests for outer attributes in expression

Adds test of issue 3904 and fix test of the issue 3874 to follows rust
1.49 behavior.

Fixes GCC-Rust/gccrs#3904

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3874.rs: Fixes test.
	* rust/compile/issue-3904.rs: New test.

Signed-off-by: lenny.chiadmi-delage <[email protected]>

Author: Villosse

gcc/testsuite/rust/compile/issue-3874.rs

@@ -1,4 +1,3 @@
 fn wow(){
     &#[serde]
-    // { dg-error "found unexpected token .#. in null denotation" "" { target *-*-* } .-1 }
-}
+} // { dg-error "found unexpected token .\}. in null denotation" "" { target *-*-* } . }

gcc/testsuite/rust/compile/issue-3904.rs

@@ -0,0 +1 @@
+static STATIC_1: dyn = *#[serde()]; // { dg-error "found unexpected token .;. in null denotation" "" { target *-*-* } 0 }