[LLVM] Prefer octal to hex for printf (#157884)

Hex escapes of the form \xff are not universally supported in the printf
implementations on the platforms that LLVM runs on (although they
apparently are in the shell builtins). Octal escapes are required to be
supported by POSIX. This patch converts all hex escapes to octal escapes
for compatibility reasons.

This came up when trying to turn on lit's internal shell by default for
llvm/. We started using /usr/bin/printf instead of the shell builtin on
MacOS, which does not support hex escapes.

I used the following python script to automate most of the conversion
with a few manual touchups needed:
```py
import sys

def process_line(to_process: str):
    output = ""
    i = 0
    while i < len(to_process):
        if to_process[i:i+2] == '\\x':
            hex_string = to_process[i+2:i+4]
            number = int(hex_string, 16)
            output += "\\"
            octal_string = oct(number)[2:]
            if len(octal_string) == 1:
                octal_string = "00" + octal_string
            elif len(octal_string) == 2:
                octal_string = "0" + octal_string
            assert(len(octal_string) == 3)
            output += octal_string
            i += 4
        else:
            output += to_process[i]
            i += 1
    return output

with open(sys.argv[1]) as input_file:
    lines = input_file.readlines()

for i, _ in enumerate(lines):
    lines[i] = process_line(lines[i])

with open(sys.argv[1], 'w') as output_file:
    output_file.writelines(lines)
```