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/calls/execve-nt.greg.c

@@ -23,6 +23,7 @@
 #include "libc/calls/ntspawn.h"
 #include "libc/calls/strace.internal.h"
 #include "libc/calls/syscall-nt.internal.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/mem/alloca.h"
 #include "libc/nt/accounting.h"
 #include "libc/nt/console.h"
@@ -59,13 +60,28 @@ textwindows int sys_execve_nt(const char *program, char *const argv[],
   int rc;
   size_t i;
   uint32_t dwExitCode;
+  char progbuf[PATH_MAX];
   struct MemoryIntervals *mm;
   struct NtStartupInfo startinfo;
   struct NtProcessInformation procinfo;
 
+  if (strlen(program) + 4 + 1 > PATH_MAX) {
+    return enametoolong();
+  }
+
   // this is a non-recoverable operation, so do some manual validation
   if (sys_faccessat_nt(AT_FDCWD, program, X_OK, 0) == -1) {
-    return eacces();
+    stpcpy(stpcpy(progbuf, program), ".com");
+    if (sys_faccessat_nt(AT_FDCWD, progbuf, X_OK, 0) != -1) {
+      program = progbuf;
+    } else {
+      stpcpy(stpcpy(progbuf, program), ".exe");
+      if (sys_faccessat_nt(AT_FDCWD, progbuf, X_OK, 0) != -1) {
+        program = progbuf;
+      } else {
+        return eacces();
+      }
+    }
   }
 
   //////////////////////////////////////////////////////////////////////////////