-ansi means -std=c89, so replace -std=gnu99 -ansi with it

third_party/yasm/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # The yasm build process creates a slew of small C subprograms that
 # dynamically generate files at various point in the build process.  This makes
 # the build integration moderately complex.
 #
 # There are three classes of dynamically generated files:
 #   1) C source files that should be included in the build (eg., lc3bid.c)
@@ skipping 269 matching lines @@
     ]
 
     # Yasm generates a bunch of .c files which its source file #include.
     # Add the |target_gen_dir| into the include path so it can find them.
     # Ideally, these generated .c files would be placed into a separate
     # directory, but the gen_x86_insn.py script does not make this easy.
     include_dirs = [ yasm_gen_include_dir ]
 
     if (!is_win) {
       cflags = [
-        "-ansi",
+        "-std=c89",
         "-pedantic",
       ]
     }
 
     # TODO(ajwong): This should take most of the generated output as
     # inputs.
     deps = [
       ":compile_gperf",
       ":compile_gperf_for_include",
       ":compile_nasm_macros",
@@ skipping 203 matching lines @@
 
     # Output eventually #included by source/patched-yasm/frontends/yasm/x86id.c
     outputs = [
       "$yasm_gen_include_dir/x86insns.c",
       "$yasm_gen_include_dir/x86insn_gas.gperf",
       "$yasm_gen_include_dir/x86insn_nasm.gperf",
     ]
     args = [ rebase_path(yasm_gen_include_dir, root_build_dir) ]
   }
 }