Incorrect behavior when configured using --without-cuda

[Paul Hargrove]

The Makefile logic for such targets as dev-check depend on UPCXX_CUDA being 1 or empty.
Currently, passing --without-cuda to configure will set a value of 0 in the generated top-level Makefile (vs. leaving it blank for no cuda option). This leads to (failing) attempts to build CUDA-specifc tests via make dev-check.

There are no known problems (nor ones suspected based on source inspection) on make targets intended for use normal use by the end-user.

[Paul Hargrove]

Fix dev-check when configured using --without-cuda

This commit corrects the behavior of make dev-check and related make targets by checking $(UPCXX_CUDA) for equality with 1 in bld/tests.mak, just as is done in bld/Makefile. This is consistent with the approach we take with #if (not #ifdef) in headers such that 0 and undefined are both "false".

Additionally, the configure logic as been updated to ensure that UPCXX_CUDA is 1 or empty, in place of the prior tri-state behavior.

Resolves issue #426

→ <<cset 2bd18cab20b4>>