system STL is not useful and should be removed #744

Description

CppReference suggests <cmath> should overload std::abs with versions taking (and returning) various floating-point types:
https://en.cppreference.com/w/cpp/numeric/math/fabs

With the system STL, this doesn't happen.

The latest NDK default compiler does generate a warning for this [though the suggested fix in the note clearly doesn't work for this STL]:

warning: using integer absolute value function 'abs' when argument is of floating point type [-Wabsolute-value]
note: use function 'std::abs' instead
note: include the header <cmath> or explicitly provide a declaration for 'std::abs'

Minimal test project:
https://github.com/tangobravo/ndk-abs-test

Commenting out the following block in app/build.gradle to show it working in with the default STL implementations:

        externalNativeBuild {
            cmake {
                arguments "-DANDROID_STL=system"
            }
        }

There are probably other cmath functions that should have overloads, but it was the abs() one that I was testing at the time when I noticed it. I realise the gnustl and stlport options are being removed, but I believe the system one is still supported as a reasonable "no STL" option (and remains the default with ndkBuild I think) so thought it worthwhile to file a bug.

Environment Details

OS X 10.12.6, Android Studio 3.0.1 [probably not important for this bug]
Using NDK bundle from Android Studio: 17.1.4828580