Fix MINGW32 errors and warnings

[legends2k]

• Include share.h for _SH_DENYNO’s definition
• Define NOMINMAX only if not already defined; MINGW warns of redefinition since bits/os_defines.h included by <algorithm> already defines it
• Use C++11 thread_local instead of the non-standard option of __declspec(thread) 1

[legends2k]

This also fixes #219.

[legends2k]

Used thread_local within LOGURU_WINTHREADS macro since both MinGW and MSVC 2015 (7+ years old now) support it.

@emilk Please let me know if you've concerns around this.