[NFC][flang] Add the test case for D125371

This adds the test case with portability warning preparing for D125804,
which supports checking for portability warnings in test_errors.py.

Reviewed By: ekieri

Differential Revision: https://reviews.llvm.org/D127821

Author: PeixinQiao

flang/test/Semantics/long-name.f90

@@ -0,0 +1,14 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+
+!WARNING: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg1 has length 64, which is greater than the maximum name length 63
+program aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg1
+
+  !WARNING: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg2 has length 64, which is greater than the maximum name length 63
+  integer :: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg2
+
+  integer :: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg
+
+  !WARNING: aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg3 has length 64, which is greater than the maximum name length 63
+  call aaaaaaaaaabbbbbbbbbbccccccccccddddddddddeeeeeeeeeeffffffffffggg3
+
+end