build: Fix --with-gcrypt-headers and --with-vorbis-headers.

build: Fix --with-gcrypt-headers and --with-vorbis-headers.

The configure script sets the autoconf output variable gcrypt_cppflags
according to the configure option --with-gcrypt-headers, but
gcrypt_cppflags is never used for the build.  Hence, if libgcrypt is
installed in a non-standard location, and that location is specified
as the argument to --with-gcrypt-headers, configure detects the gcrypt
header correctly, but the build fails nevertheless.

The same type of bug also exists for the --with-vorbis-headers option.

To fix this omission this patch sets both variables in Makefile.in
and references it in Makefile.real to compile the affected objects
with the correct flags.