Get codebase completely working with LLVM

You can now build Cosmopolitan with Clang:

    make -j8 MODE=llvm
    o/llvm/examples/hello.com

The assembler and linker code is now friendly to LLVM too.
So it's not needed to configure Clang to use binutils under
the hood. If you love LLVM then you can now use pure LLVM.

libc/runtime/program_invocation_short_name.S

@@ -19,7 +19,7 @@
 #include "libc/macros.h"
 .source	__FILE__
 
-/	Supplies basename(argv[0]) The GNU Way.
+//	Supplies basename(argv[0]) The GNU Way.
 	.initbss 400,_init_program_invocation_short_name
 program_invocation_short_name:
 	.quad	0
@@ -34,9 +34,9 @@ program_invocation_short_name:
 	mov	(%r13),%rsi		# argv[0]
 	mov	%rsi,%rcx
 1:	lodsb
-	cmp	$'/,%al
+	cmp	$'/',%al
 	cmoveq	%rsi,%rcx
-	cmp	$'\\,%al
+	cmp	$'\\',%al
 	cmoveq	%rsi,%rcx
 	test	%al,%al
 	jnz	1b