fix lint error in wgettext()

Cppcheck was complaining about the `return val.c_str()` at the end of the
`wgettext()` function. That would normally a bug since the lifetime of
`val` ends when the function returns. In this particular case that's not
true because the string is interned in a cache. Nonetheless, rather than
suppress the lint warning I decided to modify the API to be more idiomatic.

In the process of fixing the aforementioned lint warning I fixed several other
lint errors in that module.

This required making our copy of `wgetopt()` compatible with the rest of
the fish code. Specifically, by removing its local definitions of the
"_" macro so it uses the same macro used everywhere else in the fish
code. The sooner we kill the use of wide chars the better.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/common.h b/src/common.h
index e59dfc0e..07342436 100644
--- a/src/common.h
+++ b/src/common.h
@@ -226,8 +226,8 @@ void write_ignore(int fd, const void *buff, size_t count);
         return retval;                                                     \
     }
 
-/// Shorthand for wgettext call.
-#define _(wstr) wgettext(wstr)
+/// Shorthand for wgettext call in situations where a C-style string is needed (e.g., fwprintf()).
+#define _(wstr) wgettext(wstr).c_str()
 
 /// Noop, used to tell xgettext that a string should be translated, even though it is not directly
 /// sent to wgettext.