Follow new guideline: Avoid cd DIR && FOO in RUN lines.

Instead, put `FOO` on a separate run line. `cd` affects later RUN lines,
and `cd DIR && FOO` could mislead the reader that it doesn't and that's
why we needed to put both parts on one line. I added the proposed
guideline to #346.

I'm changing the existing tests before changing more tests to use `cd`
as part of this PR.

clang/test/3C/base_subdir/canwrite_constraints.c

@@ -15,14 +15,15 @@
 // (https://github.com/correctcomputation/checkedc-clang/issues/609)
 // and then re-enable diagnostic verification here.
 //
-// RUN: cd %S && 3c -alltypes -addcr -output-dir=%t.checked/base_subdir -warn-all-root-cause %s --
+// RUN: cd %S
+// RUN: 3c -alltypes -addcr -output-dir=%t.checked/base_subdir -warn-all-root-cause %s --
 // RUN: FileCheck -match-full-lines -check-prefixes=CHECK_LOWER --input-file %t.checked/base_subdir/canwrite_constraints.c %s
 // RUN: test ! -f %t.checked/canwrite_constraints.checked.h
 
 // "Higher" case: When -base-dir is set to the parent directory, we can change
 // canwrite_constraints.h, so both q and the return should become checked.
 //
-// RUN: cd %S && 3c -alltypes -addcr -base-dir=.. -output-dir=%t.checked2 %s --
+// RUN: 3c -alltypes -addcr -base-dir=.. -output-dir=%t.checked2 %s --
 // RUN: FileCheck -match-full-lines -check-prefixes=CHECK_HIGHER --input-file %t.checked2/base_subdir/canwrite_constraints.c %s
 // RUN: FileCheck -match-full-lines -check-prefixes=CHECK_HIGHER --input-file %t.checked2/canwrite_constraints.h %S/../canwrite_constraints.h
 

clang/test/3C/base_subdir/canwrite_constraints_symlink.c

@@ -20,7 +20,8 @@
 // Now 3C should know that it can't write to base_subdir_partial_defn.h because
 // the symlink goes out of the base dir.
 //
-// RUN: cd %t.base && 3c -addcr canwrite_constraints_symlink.c -- -Xclang -verify
+// RUN: cd %t.base
+// RUN: 3c -addcr canwrite_constraints_symlink.c -- -Xclang -verify
 
 // expected-error@base_subdir_partial_defn.h:1 {{3C internal error: 3C generated changes to this file even though it is not allowed to write to the file}}
 // expected-note@*:* {{-dump-unwritable-changes}}

clang/test/3C/base_subdir/canwrite_constraints_unimplemented.c

@@ -3,7 +3,8 @@
 // an error diagnostic.
 // (https://github.com/correctcomputation/checkedc-clang/issues/387)
 
-// RUN: cd %S && 3c -addcr %s -- -Xclang -verify
+// RUN: cd %S
+// RUN: 3c -addcr %s -- -Xclang -verify
 
 // expected-error@../base_subdir_partial_defn.h:1 {{3C internal error: 3C generated changes to this file even though it is not allowed to write to the file}}
 // expected-note@*:* {{-dump-unwritable-changes}}