fix exit code for gn gen failure

Bug: 380158551
Change-Id: I325b42d9366f6dc6772545f4bd5de25641e859d6
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/17920
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: David Turner <digit@google.com>
Commit-Queue: Takuto Ikuta <tikuta@google.com>

src/gn/command_gen.cc

diff --git a/src/gn/command_gen.cc b/src/gn/command_gen.cc
index c05ecd6..cf1851e 100644
--- a/src/gn/command_gen.cc
+++ b/src/gn/command_gen.cc
@@ -760,7 +760,7 @@
   // regeneration can be restarted if interrupted.
   if (command_line->HasSwitch(switches::kRegeneration)) {
     if (!commands::PrepareForRegeneration(&setup->build_settings())) {
-      return false;
+      return 1;
     }
   }