Revert "[clang] Increase the default expression nesting limit (#104717)"

This reverts commit 7597e09.

It caused several buildbot failures due to stack overflows with the
parser test.

Author: AaronBallman

clang/docs/ReleaseNotes.rst

@@ -174,8 +174,6 @@ Deprecated Compiler Flags
 Modified Compiler Flags
 -----------------------
 
-- The compiler flag `-fbracket-depth` default value is increased from 256 to 2048.
-
 - The ``-ffp-model`` option has been updated to enable a more limited set of
   optimizations when the ``fast`` argument is used and to accept a new argument,
   ``aggressive``. The behavior of ``-ffp-model=aggressive`` is equivalent

clang/include/clang/Driver/Options.td

@@ -7976,7 +7976,7 @@ def fapply_global_visibility_to_externs : Flag<["-"], "fapply-global-visibility-
   MarshallingInfoFlag<LangOpts<"SetVisibilityForExternDecls">>;
 def fbracket_depth : Separate<["-"], "fbracket-depth">,
   HelpText<"Maximum nesting level for parentheses, brackets, and braces">,
-  MarshallingInfoInt<LangOpts<"BracketDepth">, "2048">;
+  MarshallingInfoInt<LangOpts<"BracketDepth">, "256">;
 defm const_strings : BoolOption<"f", "const-strings",
   LangOpts<"ConstStrings">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option], "Use">,

clang/test/Parser/parser_overflow.c

@@ -1,5 +1,5 @@
 // RUN: not %clang_cc1 %s -fsyntax-only -DHUGE 2>&1 | FileCheck %s
-// RUN: %clang_cc1 %s -fsyntax-only
+// RUN: not %clang_cc1 %s -fsyntax-only 2>&1 | FileCheck %s
 // RUN: not %clang_cc1 %s -fsyntax-only -fbracket-depth 299 2>&1 | FileCheck %s
 // RUN: %clang_cc1 %s -fsyntax-only -fbracket-depth 300
 // RUN: not %clang %s -fsyntax-only -fbracket-depth=299 2>&1 | FileCheck %s
@@ -15,5 +15,5 @@ void foo(void) {
 #endif
 }
 
-// CHECK: fatal error: bracket nesting level exceeded maximum of {{2048|299}}
+// CHECK: fatal error: bracket nesting level exceeded maximum of {{256|299}}
 // CHECK: note: use -fbracket-depth=N to increase maximum nesting level