Log Message:
Update bearssl from version 0.3 to version 0.4

Changes from previous version:

+ New AES and GHASH implementations for POWER8 processors (provides
AES/GCM at more than 2 gigabytes per second!).

+ Improved GHASH implementation with AES-NI opcodes (pclmulqdq).

+ New Poly1305 implementation with 64 -> 128 multiplications,
available on some 64-bit architectures.

+ New "i62" big-integer code with 64 -> 128 multiplications, available
on some 64-bit architectures (RSA is much faster).

+ Some mostly cosmetic patches to support very old systems (BearSSL
now compiles and run on Debian 2.2 "potato" from 2000, with GCC
2.95).