[MC,ELF] Refactor the test

- Remove redundant `--check-prefix`
- Remove `-DFILE=`

Author: chestnykh

llvm/test/MC/ELF/warn-newline-in-escaped-string.s

@@ -1,9 +1,10 @@
-// RUN: llvm-mc -filetype=obj -triple x86_64 %s 2>&1 -o /dev/null | FileCheck -DFILE=%s --strict-whitespace %s --implicit-check-not="{{[0-9]+:[0-9]+: warning: unterminated string}}" --check-prefix=CHECK-WARN
+// RUN: llvm-mc -filetype=obj -triple x86_64 %s 2>&1 -o /dev/null \
+// RUN: | FileCheck %s --implicit-check-not="{{[0-9]+:[0-9]+: warning: unterminated string}}"
 
 .string "abcd\xFFefg
 12345678"
 
-// CHECK-WARN:   [[#@LINE-3]]:21: warning: unterminated string; newline inserted
+// CHECK:       [[#@LINE-3]]:21: warning: unterminated string; newline inserted
 // CHECK-NEXT:  .string "abcd\xFFefg
 
 .ascii "some test ascii
@@ -13,14 +14,14 @@ with
 newlines\x0A
 "
 
-// CHECK-WARN:   [[#@LINE-7]]:24: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-7]]:24: warning: unterminated string; newline inserted
 // CHECK-NEXT:   .ascii "some test ascii
-// CHECK-WARN:   [[#@LINE-8]]:1: warning: unterminated string; newline inserted
-// CHECK-WARN:   [[#@LINE-8]]:9: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-8]]:1: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-8]]:9: warning: unterminated string; newline inserted
 // CHECK-NEXT:   sequence
-// CHECK-WARN:   [[#@LINE-9]]:5: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-9]]:5: warning: unterminated string; newline inserted
 // CHECK-NEXT:   with
-// CHECK-WARN:   [[#@LINE-10]]:13: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-10]]:13: warning: unterminated string; newline inserted
 // CHECK-NEXT:   newlines\x0A
 
 .asciz "another test string
@@ -31,23 +32,23 @@ newline characters
 
 "
 
-// CHECK-WARN:   [[#@LINE-8]]:28: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-8]]:28: warning: unterminated string; newline inserted
 // CHECK-NEXT:   .asciz "another test string
-// CHECK-WARN:   [[#@LINE-9]]:1: warning: unterminated string; newline inserted
-// CHECK-WARN:   [[#@LINE-9]]:5: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-9]]:1: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-9]]:5: warning: unterminated string; newline inserted
 // CHECK-NEXT:   with
-// CHECK-WARN:   [[#@LINE-10]]:19: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-10]]:19: warning: unterminated string; newline inserted
 // CHECK-NEXT:   newline characters
-// CHECK-WARN:   [[#@LINE-11]]:1: warning: unterminated string; newline inserted
-// CHECK-WARN:   [[#@LINE-11]]:1: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-11]]:1: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-11]]:1: warning: unterminated string; newline inserted
 
 .file "warn-newline
 .s"
-// CHECK-WARN:   [[#@LINE-2]]:20: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-2]]:20: warning: unterminated string; newline inserted
 
 .cv_file 1 "some_an
 other_file.s"
-// CHECK-WARN:   [[#@LINE-2]]:20: warning: unterminated string; newline inserted
+// CHECK:        [[#@LINE-2]]:20: warning: unterminated string; newline inserted
 
 .ascii "test\nvalid1_string\xFF\n\n\xFF"
 .asciz "\n\n\nvalid2_string\x0A"