std::min requires 2 matching parameters

[jmjatlanta]

On macOS, size_t is an unsigned long long. std::min does not do implicit conversions, and fails to compile certain fc:: headers.

Build Error Description
build error stating it cannot find an appropriate template for std::min

Build Environment
Details about the build environment, including the relevant required libraries. Much of this information can be found in the CMakeFiles/CMakeOutput.log.

• Host OS: macOS 10.14 (Mojave)
• Host Physical RAM 8GB
• Source Branch/Tag: develop
• OpenSSL Version: 1.1.0h
• Boost Version: 1.68.0
• C++ Compiler: clang

Steps To Reproduce
Attempt to compile bitshares-fc on macOS

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