[flang][nfc] Port 2 tests to use the new driver when enabled

This is similar to https://reviews.llvm.org/D100309, i.e. `%f18` is
replaced with `%flang_new`.

resolve105.f90 wasn't in tree when D100309 was worked on, so it's
updated here instead.

label14.f90 requires `-fsyntax-only`. I didn't notice that when
submitting D100309, hence updating it now instead. `-fsyntax-only` is
required to prevent `%f18` from calling an external compiler (which then
fails and returns a non-zero exit code).

Differential Revision: https://reviews.llvm.org/D100655

flang/test/Semantics/label14.f90

@@ -2,7 +2,7 @@
 ! 11.1.4 - 4 It is permissible to branch to and end-block-stmt only withinh its
 !            Block Construct
 
-! RUN: not %f18 %s 2>&1 | FileCheck %s
+! RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
 ! CHECK: Label '20' is not in scope
 
 subroutine s1

flang/test/Semantics/resolve105.f90

@@ -1,4 +1,4 @@
-! RUN: %S/test_errors.sh %s %t %f18
+! RUN: %S/test_errors.sh %s %t %flang_fc1
 ! Test instantiation of components that are procedure pointers.
 ! 
 program test