Improve C99 compliance for wider compiler support

[hashpling]

This range of commits improves C99 compliance and as a result allows tig to be compiled with the native compilers on Solaris (SunStudio cc) and AIX (xlc).

[jonas]

Wow, thanks. Nice patch set. The travis build shows two warnings which are trivial to fix. Unless you want to update the pull request, I can do these two touch ups as well as adding an entry to the NEWS file before merging.

src/prompt.c:860:21: warning: suggest braces around initialization of subobject
      [-Wmissing-braces]
                struct key key = {0};
                                  ^
                                  {}

src/main.c:96:26: warning: suggest braces around initialization of subobject
      [-Wmissing-braces]
        struct commit commit = {0};
                                ^
                                {}

[hashpling]

I guess it's looking for struct commit commit = {{0}}; or even {""};. To me, plain {0} is idiomatic C and "double bracing" looks a bit ugly. Note that this warning should go away in a newer version of gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53119 .

[hashpling]

So I tested with {{0}} in both places and both native compilers are happy so it's up to you. If a warning-free travis is important to you then I don't object to these touch ups even though I think it's a bogus warning in this case.

[jonas]

What is important is that make all-debug which adds -Wall to CFLAGS works for me locally and it does not. So I will add the missing braces.

[jonas]

Thanks merged.

It's probably time to embrace more C99 constructs in the code base, especially for struct initialization. This is a good start!

[hashpling]

Thanks! I'll test with all-debug, at least on Linux, for any further patches which I come up with.