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/getntsyspath.S

@@ -16,6 +16,7 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/dce.h"
 #include "libc/macros.internal.h"
 
 //	Obtains WIN32 magic path, e.g. GetTempPathA.
@@ -33,7 +34,13 @@ __getntsyspath:
 	movpp	%rdi,%rcx		# call f=%rax(p1=%rcx,p2=%rdx)
 	sub	$40,%rsp
 	call	*%rax
-	xor	%edx,%edx
+	testb	IsWindows()
+	jz	3f
+	mov	(%rdi),%cl		# turn c:\... into \c\...
+	movb	$'\\',(%rdi)
+	mov	%cl,1(%rdi)
+	movb	$'\\',2(%rdi)
+3:	xor	%edx,%edx
 	mov	-8(%rbp),%ecx		# restore %edx param as %ecx
 	cmp	%eax,%ecx		# use current dir on overflow
 	cmovbe	%edx,%eax