Make build hermetic without shell scripts

- Fix some minor issues in ar.com
- Have execve() look for `ape` command
- Rewrite NT paths using /c/ rather /??/c:/
- Replace broken GCC symlinks with .sym files
- Rewrite $PATH environment variables on startup
- Make $(APE_NO_MODIFY_SELF) the default bootloader
- Add all build command dependencies to build/bootstrap
- Get the repository mostly building from source on non-Linux

libc/x/xfixpath.c

@@ -0,0 +1,63 @@
+/*-*- 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 2022 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 "libc/mem/mem.h"
+#include "libc/runtime/runtime.h"
+#include "libc/str/str.h"
+#include "libc/x/x.h"
+
+static inline int IsAlpha(int c) {
+  return ('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z');
+}
+
+/**
+ * Fixes $PATH environment variable on Windows.
+ */
+void xfixpath(void) {
+  size_t i;
+  char *p, *path;
+  path = strdup(getenv("PATH"));
+  if (strstr(path, "C:\\") && strstr(path, ";")) {
+
+    // turn backslash into slash
+    for (p = path; *p; ++p) {
+      if (*p == '\\') *p = '/';
+    }
+
+    // turn c:/... into /c/...
+    if (IsAlpha(path[0]) && path[1] == ':' && path[2] == '/') {
+      path[1] = path[0];
+      path[0] = '/';
+    }
+    for (p = path, i = 0; p[i]; ++i) {
+      if (p[i + 0] == ';' && IsAlpha(p[i + 1]) && p[i + 2] == ':' &&
+          p[i + 3] == '/') {
+        p[i + 2] = p[i + 1];
+        p[i + 1] = '/';
+      }
+    }
+
+    // turn semicolon into colon
+    for (p = path; *p; ++p) {
+      if (*p == ';') *p = ':';
+    }
+
+    setenv("PATH", path, true);
+  }
+  free(path);
+}