win32: add env var to control error dialogs

If the environment variable BB_CRITICAL_ERROR_DIALOGS is set to
1 critical error dialogs are enabled.  If unset or set to any
other value they aren't.  In either case the error messages
introduced by commit 790e37727 (win32: revert 'don't set error
mode') are issued.

The shell exports BB_CRITICAL_ERROR_DIALOGS to the environment
immediately on any change so the setting takes effect at once.

Adds 104-160 bytes.

(GitHub issue #423)

2 files changed, 3 insertions, 2 deletions

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index c90285ae9..121959376 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -1352,7 +1352,7 @@ int main(int argc UNUSED_PARAM, char **argv)
 
         /* Have this process handle critical errors itself:  the default
          * system-generated error dialogs may be inconvenient. */
-        SetErrorMode(SEM_FAILCRITICALERRORS);
+        change_critical_error_dialogs(getenv(BB_CRITICAL_ERROR_DIALOGS) ?: "");
 #endif
 
 #if defined(__MINGW64_VERSION_MAJOR)
diff --git a/libbb/messages.c b/libbb/messages.c
index 12079a2e0..27ba244d6 100644
--- a/libbb/messages.c
+++ b/libbb/messages.c
@@ -47,7 +47,8 @@ const char bbvar[] ALIGN1 =
                 "BB_OVERRIDE_APPLETS\0" \
                 "BB_SKIP_ANSI_EMULATION\0" \
                 "BB_TERMINAL_MODE\0" \
-                "BB_SYSTEMROOT\0";
+                "BB_SYSTEMROOT\0" \
+                "BB_CRITICAL_ERROR_DIALOGS\0";
 #endif
 const char bb_default_login_shell[] ALIGN1 = LIBBB_DEFAULT_LOGIN_SHELL;
 /* util-linux manpage says /sbin:/bin:/usr/sbin:/usr/bin,