Make util compilable with C++

[jokva]

Task

Compile util with g++

Approach

Renamed all util/*.c files to .cpp and compiled with g++. Lots of errors, most of them crying about implicit void* casts.

As a consequence, some extern Cs are added and fixed.

The patch isn't warning free with C++, but does compile and tests do work.

Pre un-WIP checklist

• Statoil tests pass locally

[joakim-hove]

Will it continue to build and compile with C - or is this a one-way-street?

[jokva]

It's still valid C, and it will be for quite a while.

[jokva]

Oh, and I should add, the first commit in this series fixes a problem with the version_* functions returning non-const pointers to static strings, which is a violation in C++. I don't think it is in C, but it should be cleaned up anyway. It shouldn't break binary compatibility in any way, unless downstream users assign these to non-const pointers (which, I'd argue, was always a bug).

[joakim-hove]

As I understand it: These are changes to the source and header files which allow compilation with a C++ compiler, but the build system will still compile as C? In that case this should be merged right away - as soon as the merge conflict is resolved.

[jokva]

As I understand it: These are changes to the source and header files which allow compilation with a C++ compiler, but the build system will still compile as C? In that case this should be merged right away - as soon as the merge conflict is resolved.

100% correct.

[jokva]

Travis didn't want to restart.