CMake/CRYPTO - set CMAKE_REQUIRED_INCLUDES

[justsmth]

When using a custom CRYPTO library, that library's include path should be set to the CMAKE_REQUIRED_INCLUDES prior to check_include_file.

CMAKE_REQUIRED_INCLUDES
A ;-list of header search paths to pass to the compiler. These will be the only header search paths used--the contents of the INCLUDE_DIRECTORIES directory property will be ignored.

Testing

• Setup

cd `mktemp -d`
git clone https://github.com/aws/aws-lc.git
git clone https://github.com/the-tcpdump-group/tcpdump.git
# Then... change branch or apply this PR as a patch to tcpdump

• Build/Install AWS-LC

mkdir aws-lc-build aws-lc-install
cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=./aws-lc-install -B ./aws-lc-build -S ./aws-lc
cmake --build ./aws-lc-build --target install -j 4

• Build tcpdump -- (CMAKE_PREFIX_PATH needs to be set to an absolute path.)

mkdir -p tcpdump-build
cmake -DCMAKE_BUILD_TYPE=Debug -DCMAKE_PREFIX_PATH=`pwd`/aws-lc-install -S ./tcpdump -B ./tcpdump-build
cmake --build ./tcpdump-build --target tcpdump
cmake --build ./tcpdump-build --target check

Several tests may fail until PR #1351 is merged.

[justsmth]

I updated the description to show how to setup the build to use (e.g.) AWS-LC.