Fix build with newer gcc versions.

Add upstream patch [1] that uses

• math.h -> cmath
• isnan() -> std::isnan()

This fixes compilation with gcc5.

[1] https://quickgit.kde.org/?p=marble.git&a=commit&h=486f6181d6fef15c9b6c72504e3588be502bea80

PR: 213995
Reported by: Kenneth Salerno <kennethsalerno@yahoo.com>
Approved by: rakuco (mentor)
Obtained from: https://quickgit.kde.org/?p=marble.git&a=commit&h=486f6181d6fef15c9b6c72504e3588be502bea80