Cannot deal with non-ASCII preprocessor output

[arsdragonfly]

Currently the gcc preprocessor output varies depending on the language set. On my system, this is what a short c program's output looks like:

⚡ gcc -E test.c
# 1 "test.c"
# 1 "<built-in>"
# 1 "<命令行>"
# 31 "<命令行>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<命令行>" 2
# 1 "test.c"
int main()
{
 return 0;
}

and c2hs can't process it due to not being able to handle non-ascii characters in line 3, 4 and 6. See #237 .

if we override the environment variable LANG, we get

⚡ LANG=ASCII gcc -E test.c
# 1 "test.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<command-line>" 2
# 1 "test.c"
int main()
{
 return 0;
}

which works correctly.

This bug is breaking every test case and causing more problems downstream (every package that depends on c2hs is failing to build right now). I suppose it has something to do with takeChar's implementation.

[arsdragonfly]

Prelude.head: empty list error appears on international locales; needs export LANG=C as workaround.