CMake pthread lookup breaking build about indi

[TallFurryMan]

indi@astro1:~/indi_dev/indi$ cmake --version
cmake version 3.6.3

CMake suite maintained and supported by Kitware (kitware.com/cmake).

[TallFurryMan]

Switch "-Werror" causes CMake 3.6.3's source snippet checking for pthread.h to fail.
The problem occurs because of the redefinition of _FORTIFY_SOURCE, defined internally by gcc 4.9.4 on Gentoo.

Often cited solution is to undefine "_FORTIFY_SOURCE" before defining it again on the command line. No very elegant, but effective.

I'll provide a pull request, merge as you wish.

[TallFurryMan]

Offering to fix with PR #261.

[TallFurryMan]

I had a look. In my case cmake was not using optimization when checking for pthread, whatever the configuration. I'll double check but I think my pull request is still necessary for both libindi and 3rdparty. Of course, in my situation, _FORTIFY_SOURCE is predefined to 2 by gcc, so we loose nothing.

[kecsap]

@TallFurryMan: Can you send me your cmake error log (CMakeError.txt or CMakeError.log) to my email. I am curious: [email protected]

[TallFurryMan]

Ah, just deleted the build tree to restart a dark library with bleeding edge.
The initial error was a #warning, stating _FORTIFY_SOURCE was redefined, as gcc 4.9.4 predefines it.
The second error was also a #warning, stating _FORTIFY_SOURCE had to be used with optimization, as cmake was not checking for pthread with that. I didn't test yet with the manual addition of -O1, but I think I remember it was not using the C flags. Probably pthread was a lone case.
I'll reproduce and let you know.

[kecsap]

Now I see. Your PR really fixes the problem properly.