I wanted to make sure clang is used as a compiler for clang builds.
And my test (after chmod a-x /usr/bin/gcc) with make distclean; make -f Makefile.orig (and then checking for *.o files in src/escrypt) suggests I succeeded.

If the make is triggered from the global src directory, $(CC) will get passed from the main make process and not be overwritten with "gcc".
OTOH, if you run 
```
make -f Makefile.orig
```
directly from src/escrypt/, i.e., without a parent make process, $(CC) will be set to "cc". /usr/bin/cc is a symbolic link to /usr/bin/gcc on my system.