[goalc] Fix some small issues with float to int

[water111]

It turns out I did not read the manual close enough, and our behavior with floats/ints was not correct.

I think the only likely way this could have gone wrong is if you have code that does fpr -> gpr, then expects the fpr to sign extend and does a (64-bit) slt.

[coveralls]

Pull Request Test Coverage Report for Build 1188258707

• 15 of 19 (78.95%) changed or added relevant lines in 6 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 64.509%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
goalc/compiler/compilation/Function.cpp	1	3	33.33%
goalc/compiler/compilation/Type.cpp	1	3	33.33%

Totals
Change from base Build 1187989119:	0.003%
Covered Lines:	39837
Relevant Lines:	61754

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💛 - Coveralls