Fix shared build

[gadoofou87-zz]

Fixes #108

[Mizux]

also related to #108 we should add CMP0077

At the beginning of the file:

# option() honors normal variables.
# see: https://cmake.org/cmake/help/latest/policy/CMP0077.html
if(POLICY CMP0077)
  cmake_policy(SET CMP0077 NEW)
endif()

thus passing -DBUILD_PIC=ON won't be overwritten by CMake...