Validate privileged code relationships

- Work towards improving non-optimized build support
- Introduce MODE=zero which is -O0 without ASAN/UBSAN
- Use system GCC when ~/.cosmo.mk has USE_SYSTEM_TOOLCHAIN=1
- Have package.com check .privileged code doesn't call non-privileged

libc/intrin/strerror_wr.greg.c

@@ -16,10 +16,10 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#define ShouldUseMsabiAttribute() 1
 #include "libc/dce.h"
 #include "libc/fmt/fmt.h"
 #include "libc/intrin/kprintf.h"
-#include "libc/intrin/safemacros.internal.h"
 #include "libc/macros.internal.h"
 #include "libc/nt/enum/formatmessageflags.h"
 #include "libc/nt/enum/lang.h"
@@ -39,8 +39,14 @@ privileged int strerror_wr(int err, uint32_t winerr, char *buf, size_t size) {
   char16_t winmsg[256];
   const char *sym, *msg;
   wanting = false;
-  sym = firstnonnull(_strerrno(err), (wanting = true, "EUNKNOWN"));
-  msg = firstnonnull(_strerdoc(err), (wanting = true, "No error information"));
+  if (!(sym = _strerrno(err))) {
+    sym = "EUNKNOWN";
+    wanting = true;
+  }
+  if (!(msg = _strerdoc(err))) {
+    msg = "No error information";
+    wanting = true;
+  }
   if (IsTiny()) {
     if (!sym) sym = "EUNKNOWN";
     for (; (c = *sym++); --size)
@@ -49,7 +55,7 @@ privileged int strerror_wr(int err, uint32_t winerr, char *buf, size_t size) {
   } else if (!IsWindows() || ((err == winerr || !winerr) && !wanting)) {
     ksnprintf(buf, size, "%s/%d/%s", sym, err, msg);
   } else {
-    if ((n = FormatMessage(
+    if ((n = __imp_FormatMessageW(
              kNtFormatMessageFromSystem | kNtFormatMessageIgnoreInserts, 0,
              winerr, MAKELANGID(kNtLangNeutral, kNtSublangDefault), winmsg,
              ARRAYLEN(winmsg), 0))) {