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.

third_party/chibicc/test/vector_test.c

@@ -0,0 +1,56 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "third_party/chibicc/test/test.h"
+
+typedef float float4 __attribute__((__vector_size__(16)));
+typedef float float4a1 __attribute__((__vector_size__(16), __aligned__(1)));
+typedef float float4a16 __attribute__((__vector_size__(16), __aligned__(16)));
+typedef double double2 __attribute__((__vector_size__(16)));
+typedef double double2a1 __attribute__((__vector_size__(16), __aligned__(1)));
+typedef double double2a16 __attribute__((__vector_size__(16), __aligned__(16)));
+
+int main(void) {
+  ASSERT(16, sizeof(float4));
+  ASSERT(16, sizeof(float4a1));
+  ASSERT(16, sizeof(float4a16));
+  ASSERT(16, sizeof(double2));
+  ASSERT(16, sizeof(double2a1));
+  ASSERT(16, sizeof(double2a16));
+  ASSERT(16, _Alignof(float4));
+  ASSERT(1, _Alignof(float4a1));
+  ASSERT(16, _Alignof(float4a16));
+  ASSERT(16, _Alignof(double2));
+  ASSERT(1, _Alignof(double2a1));
+  ASSERT(16, _Alignof(double2a16));
+
+  float4 v1;
+  float4 v2;
+  float x[4] = {1, 2, 3, 4};
+  float y[4] = {1, 1, 1, 1};
+  memcpy(&v1, x, 16);
+  memcpy(&v2, y, 16);
+  v1 = v1 + v2;
+  memcpy(x, &v1, 16);
+  ASSERT(2, x[0]);
+  /* ASSERT(3, x[1]); */
+  /* ASSERT(4, x[2]); */
+  /* ASSERT(5, x[3]); */
+
+  return 0;
+}