Amalgamated build requires pkcs11.h

[ghost]

Amalgamated build requires pkcs11.h, which, in turn, requires a bunch of other stuff.

Repro (on a recent Intel Xeon):

git clone https://github.com/randombit/botan.git
cd botan
./configure.py --amalgamation --single-amalgamation-file
g++ -std=c++11 botan_all.cpp

Result:

In file included from botan_all.cpp:8:0:
botan_all.h:19302:20: fatal error: pkcs11.h: No such file or directory
compilation terminated.

Expected result:

*.cpp should compile and produce an object file.