Fix throw with exceptions disabled and improve noexception test

[phprus]

throw replaced with FMT_THROW in chrono.h.
Improve noexception test.

[alexezeder]

We can probably change noexception-test to include all headers. This way, it would also fail for commits like eab2ea9.

[alexezeder]

It looks like GCC doesn't care about throw in headers with exceptions disabled with no usage in cpp file. But at least Clang cares.

[vitaut]

Thank you!