[mypyc] Implement float abs primitive (#9695)

Related to mypyc/mypyc#644, also part of the plan to speed up rest of 
the slow microbenmark ops

Implement builtins.abs on float.

mypyc/primitives/float_ops.py

@@ -15,3 +15,11 @@
     return_type=float_rprimitive,
     c_function_name='PyFloat_FromString',
     error_kind=ERR_MAGIC)
+
+# abs(float)
+c_function_op(
+    name='builtins.abs',
+    arg_types=[float_rprimitive],
+    return_type=float_rprimitive,
+    c_function_name='PyNumber_Absolute',
+    error_kind=ERR_MAGIC)

mypyc/test-data/fixtures/ir.py

@@ -82,6 +82,7 @@ def __add__(self, n: float) -> float: pass
     def __sub__(self, n: float) -> float: pass
     def __mul__(self, n: float) -> float: pass
     def __truediv__(self, n: float) -> float: pass
+    def __neg__(self) -> float: pass
 
 class complex:
     def __init__(self, x: object, y: object = None) -> None: pass
@@ -251,6 +252,7 @@ def zip(x: Iterable[T], y: Iterable[S]) -> Iterator[Tuple[T, S]]: ...
 @overload
 def zip(x: Iterable[T], y: Iterable[S], z: Iterable[V]) -> Iterator[Tuple[T, S, V]]: ...
 def eval(e: str) -> Any: ...
+def abs(x: float) -> float: ...
 
 # Dummy definitions.
 class classmethod: pass

mypyc/test-data/run-floats.test

@@ -10,3 +10,11 @@ assert str_to_float("1.234567") == 1.234567
 assert str_to_float("44324") == 44324.0
 assert str_to_float("23.4") == 23.4
 assert str_to_float("-43.44e-4") == -43.44e-4
+
+[case testFloatAbs]
+def test_abs() -> None:
+    assert abs(0.0) == 0.0
+    assert abs(-1.234567) == 1.234567
+    assert abs(44324.732) == 44324.732
+    assert abs(-23.4) == 23.4
+    assert abs(-43.44e-4) == 43.44e-4