The patch attached adds an option to allow the user to disable tests.
This can be useful for example when the toolchain does not provide thread.
Indeed, in this case, libgcrypt fails to build t-lock:
```
t-lock.c: In function 'run_test':
t-lock.c:359:3: error: unknown type name 'pthread_t'
pthread_t rthread;
```
Fixes:
- http://autobuild.buildroot.org/results/50a8ba572e3fafd3c6a39bd54bcfcaf78b5ad325{F850424}