HDFFV-8937:
There is an interface incompatibility in the C library due to the renamed symbols in H5Ppublic.h.

Solution:
Bump the library interface version on the shared libraries (soname).

Tested: h5committested.
HDFFV-8933:
Did not provide default values for clang++ options.
Also, applied wrong values for the *_CPPFLAGS.

Solution:
Added default values for *_CXXFLAGS.
Fixed the *_CPPFLAGS values.

Tested: duck, swallow, quail with --eanble-production.