[compiler-rt][aarch64] New tests for 128-bit floating-point builtins, fixes of tests and __fixuint

Summary:
The following tests for 128-bit floating-point type behaved in a strange way, thought it were bugs, but seem to be mistakes in tests:

 * `fixtfsi` test checked for `0x80000001` as a value returned for number less than can be represented, while `LONG_MIN` should be returned on saturation;
 * `fixunstfdi` wasn't enabled for AArch64, only for PPC, but there is nothing PPC specific in that test;
 * `multf3` tried to underflow multiplication by producing result with 16383 exponent, while there are still 112 bits of fraction plus implicit bit, so resultant exponent should be 16497.

Tests for some other builtins didn't exist:

 * `fixtfdi`
 * `fixtfti`
 * `fixunstfti`

They were made by copying similar files and adjusting for wider types and adding/removing some reasonable/extra checks.

Also `__fixuint` seems to have off by one error, updated tests to catch this case.

Reviewers: rengolin, zatrazz, howard.hinnant, t.p.northover, jmolloy, enefaim

Subscribers: aemerson, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D14187

llvm-svn: 252180