Use cmake message WARNING and SEND_ERROR when appropriate

[scpeters]

When compiling with colcon, messages to stdout (such as message(STATUS) calls from cmake) are not displayed on the console, while messages to stderr (such as message(WARNING) and message(SEND_ERROR)) are displayed, which makes it much easier to spot configuration issues. I noticed that many places there are message(STATUS) calls notifying when optional dependencies could not be found, so I changed those to message(WARNING). I also noticed one place in DARTFindassimp.cmake (e4ca1a8) that seemed like it should cause the build to fail, so I changed that from message(STATUS) to message(SEND_ERROR).

---

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[scpeters]

I think ASSIMP_VERSION is not being set on windows?

[scpeters]

Yeah, I guess it's only detecting the version with pkg-config, which isn't available on windows. I can revert that change or add an if(NOT WIN32)

[jslee02]

It seems assimp 4.1 installs assimp-config.cmake and AssimpConfigVersion.cmake (on Windows as well). We could use config file on Windows instead of module file provided by DART by changing this line to:

if(WIN32)
  find_package(assimp REQUIRED CONFIG)
else()
  find_package(assimp REQUIRED MODULE)
endif()

I'm not sure if using the version config file would change the version variable name to ASSIMP_PACKAGE_VERSION because of this line. If so DARTFindassimp.cmake should set ASSIMP_VERSION to ASSIMP_PACKAGE_VERSION becuase ASSIMP_VERSION is used in other places.

[scpeters]

It looks like xenial has assimp 3.2, which has the cmake config files:

• https://packages.ubuntu.com/xenial/amd64/libassimp-dev/filelist

[scpeters]

I'll split the assimp change to a separate pull request

[codecov]

Codecov Report

Merging #1401 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1401      +/-   ##
==========================================
+ Coverage   57.27%   57.28%   +0.01%     
==========================================
  Files         366      366              
  Lines       27432    27483      +51     
==========================================
+ Hits        15711    15743      +32     
- Misses      11721    11740      +19

Impacted Files	Coverage Δ
dart/dynamics/IkFast.cpp	59.11% <0%> (-24.1%)	⬇️
dart/constraint/SoftContactConstraint.cpp	0% <0%> (ø)	⬆️
dart/utils/urdf/DartLoader.cpp	78.83% <0%> (+0.74%)	⬆️
dart/constraint/JointConstraint.cpp	9.8% <0%> (+0.87%)	⬆️
dart/constraint/ContactConstraint.cpp	73.05% <0%> (+1.07%)	⬆️
dart/constraint/JointLimitConstraint.cpp	67.68% <0%> (+2%)	⬆️
dart/dynamics/SharedLibraryIkFast.cpp	52.74% <0%> (+3.33%)	⬆️
dart/constraint/JointCoulombFrictionConstraint.cpp	85.32% <0%> (+3.74%)	⬆️
dart/constraint/MimicMotorConstraint.cpp	83.76% <0%> (+4.08%)	⬆️
dart/constraint/ServoMotorConstraint.cpp	82.56% <0%> (+4.3%)	⬆️
... and 1 more

[scpeters]

Sorry I saw an inconsistent warning message, so I updated it in 22a2fc7