This matches the std::numeric_limits<> method name. Negative infinity
can be obtained using -infinity() just like in C++.

Also replace the use of C99 INFINITY with the C++ constant.

Bug: b/140302841
Change-Id: Ifd5e5d1fa4fa2d9ccce6d334af22903ea7597a69
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40148
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>