Workaround differences between libc and libstd string stream parsing of float/doubles.
libc and libstd differ on how they parse strings. This has a remote chance of breaking mods and 0 A.D. code, and it broke tests on MacOS.
Add a workaround to ensure they are consistent.
Comments by: vladislavbelov
Fixes #2780
Differential Revision: https://code.wildfiregames.com/D1988