Add a "colocated" flag to symbol references. (#298)

This adds a "colocated" flag to function and symbolic global variables which
indicates that they are defined along with the current function, so they can
use PC-relative addressing.

This also changes the function decl syntax; the name now always precedes the
signature, and the "function" keyword is no longer included.

lib/cretonne/meta/base/predicates.py

@@ -0,0 +1,35 @@
+"""
+Cretonne predicates that consider `Function` fields.
+"""
+from cdsl.predicates import FieldPredicate
+from .formats import UnaryGlobalVar
+
+try:
+    from typing import TYPE_CHECKING
+    if TYPE_CHECKING:
+        from cdsl.formats import FormatField  # noqa
+except ImportError:
+    pass
+
+
+class IsColocatedFunc(FieldPredicate):
+    """
+    An instruction predicate that checks the referenced function is colocated.
+    """
+
+    def __init__(self, field):
+        # type: (FormatField) -> None
+        super(IsColocatedFunc, self).__init__(
+            field, 'is_colocated_func', ('func',))
+
+
+class IsColocatedData(FieldPredicate):
+    """
+    An instruction predicate that checks the referenced data object is
+    colocated.
+    """
+
+    def __init__(self):
+        # type: () -> None
+        super(IsColocatedData, self).__init__(
+            UnaryGlobalVar.global_var, 'is_colocated_data', ('func',))