The former was deprecated with C++14. The standard says they are the same:

The contents of the header<csignal>are the same as the C standard library
header<signal.h>.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

`__linux` is the deprecated non-standard macros which appears to be
not present at all on PowerPC.

Closes #398

Fixes the NFS client build, closes #305.

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

It does not do much harm - but it causes an unnecessary (failing)
system call.

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.