Add chibicc

This program popped up on Hacker News recently. It's the only modern
compiler I've ever seen that doesn't have dependencies and is easily
modified. So I added all of the missing GNU extensions I like to use
which means it might be possible soon to build on non-Linux and have
third party not vendor gcc binaries.

libc/calls/fileexists.c

@@ -18,6 +18,7 @@
 │ 02110-1301 USA                                                               │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
+#include "libc/calls/internal.h"
 #include "libc/calls/struct/stat.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
@@ -33,12 +34,18 @@
  * function. The stat() function may be used to differentiate them.
  */
 bool fileexists(const char *path) {
-  /* TODO(jart): Use fast path on NT? */
+  int rc, olderr;
   struct stat st;
-  int olderr = errno;
-  int rc = stat(path, &st);
-  if (rc == -1 && (errno == ENOENT || errno == ENOTDIR)) {
-    errno = olderr;
+  uint16_t path16[PATH_MAX];
+  if (!IsWindows()) {
+    olderr = errno;
+    rc = stat(path, &st);
+    if (rc == -1 && (errno == ENOENT || errno == ENOTDIR)) {
+      errno = olderr;
+    }
+    return rc != -1;
+  } else {
+    if (__mkntpath(path, path16) == -1) return -1;
+    return GetFileAttributes(path16) != -1u;
   }
-  return rc != -1;
 }

libc/calls/fstat-nt.c

@@ -34,8 +34,8 @@
 textwindows int fstat$nt(int64_t handle, struct stat *st) {
   int filetype;
   uint64_t actualsize;
-  struct NtByHandleFileInformation wst;
   struct NtFileCompressionInfo fci;
+  struct NtByHandleFileInformation wst;
   if (GetFileInformationByHandle(handle, &wst)) {
     memset(st, 0, sizeof(*st));
     filetype = GetFileType(handle);

libc/calls/internal.h

@@ -198,12 +198,12 @@ i32 tunefd$sysv(i32, i32, i32, i32) hidden;
 u32 fprot2nt(i32, i32) hidden;
 u32 prot2nt(i32, i32) privileged;
 void __restore_rt() hidden;
-void __sigenter$xnu(void *, i32, i32, void *, void *) hidden noreturn;
+void __sigenter$xnu(void *, i32, i32, void *, void *) hidden wontreturn;
 int utimensat$xnu(int, const char *, const struct timespec *, int) hidden;
 int nanosleep$xnu(const struct timespec *, struct timespec *) hidden;
 void stat2linux(void *) hidden;
 void xnutrampoline(void *, i32, i32, const struct __darwin_siginfo *,
-                   const struct __darwin_ucontext *) hidden noreturn;
+                   const struct __darwin_ucontext *) hidden wontreturn;
 
 /*───────────────────────────────────────────────────────────────────────────│─╗
 │ cosmopolitan § syscalls » windows nt » veneers                           ─╬─│┼

libc/calls/isatty.c

@@ -27,7 +27,7 @@
  * @asyncsignalsafe
  */
 bool32 isatty(int fd) {
-  char buf[sizeof(uint16_t) * 4] aligned(2);
+  char buf[sizeof(uint16_t) * 4] forcealign(2);
   if (!IsWindows()) {
     return ioctl$sysv(fd, TIOCGWINSZ, &buf) != -1;
   } else {

libc/calls/struct/sigaction.h

@@ -14,7 +14,7 @@ struct sigaction { /* cosmo abi */
   void (*sa_restorer)(void);
   struct sigset sa_mask;
   int64_t __pad;
-} aligned(8);
+} forcealign(8);
 
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_SIGACTION_H_ */

libc/calls/struct/siginfo.h

@@ -49,7 +49,7 @@ struct siginfo {
     };
     char __ignoreme[128 - 2 * sizeof(int32_t) - sizeof(int64_t)];
   };
-} aligned(8);
+} forcealign(8);
 
 typedef struct siginfo siginfo_t;
 

libc/calls/xnutrampoline.c

@@ -425,9 +425,9 @@ static void xnussefpustate2linux(struct FpuState *fs,
   memcpy(fs->st, &xnufs->__fpu_stmm0, (8 + 16) * sizeof(uint128_t));
 }
 
-noreturn void xnutrampoline(void *fn, int infostyle, int sig,
-                            const struct __darwin_siginfo *xnuinfo,
-                            const struct __darwin_ucontext *xnuctx) {
+wontreturn void xnutrampoline(void *fn, int infostyle, int sig,
+                              const struct __darwin_siginfo *xnuinfo,
+                              const struct __darwin_ucontext *xnuctx) {
   /* note: this function impl can't access static memory */
   intptr_t ax;
   struct Goodies {