Fix breakages in Linux-only build modes

- compile.com now polyfills -march=native which gcc/clang removed
- Guarantee zero Windows code is linked into non-Windows binaries
- MODE=tinylinux binaries are now back to being as tiny as ~4kb
- Improve the runtime's stack allocation / alignment hack
- GitHub Actions now tests Linux modes for assurance

libc/errno.h

@@ -9,7 +9,7 @@ COSMOPOLITAN_C_START_
  */
 
 #if defined(__GNUC__) && defined(__x86_64__) && defined(__MNO_RED_ZONE__) && \
-    !defined(__STRICT_ANSI__)
+    !defined(__STRICT_ANSI__) && !defined(__cplusplus)
 #define errno                                                           \
   (*({                                                                  \
     errno_t *_ep;                                                       \