gnu: Update ldc to 0.17.1.

* gnu/packages/ldc.scm (ldc): Changed.
* gnu/packages/patches/ldc-0.17.1-disable-tests.patch: New patch.
---
 gnu/packages/ldc.scm                               | 25 ++++---
 .../patches/ldc-0.17.1-disable-tests.patch         | 86 ++++++++++++++++++++++
 2 files changed, 101 insertions(+), 10 deletions(-)
 create mode 100644 gnu/packages/patches/ldc-0.17.1-disable-tests.patch