Merge #203: cmake: search capnproto in package mode only

3bee07a cmake: search capnproto in package mode only (Daniel Pfeifer)

Pull request description:

  CMake does not provide a `FindCapnProto.cmake` module and never will, because CapnProto already ships CMake package configuration files. Make sure to skip the search for the CMake module and avoid the confusing "By not providing ..." error message if CapnProto is not installed.

  Current error message if CapnProto is not intalled:
  ```
  CMake Error at CMakeLists.txt:16 (find_package):
    By not providing "FindCapnProto.cmake" in CMAKE_MODULE_PATH this project
    has asked CMake to find a package configuration file provided by
    "CapnProto", but CMake did not find one.

    Could not find a package configuration file provided by "CapnProto"
    (requested version 0.7) with any of the following names:

      CapnProtoConfig.cmake
      capnproto-config.cmake

    Add the installation prefix of "CapnProto" to CMAKE_PREFIX_PATH or set
    "CapnProto_DIR" to a directory containing one of the above files.  If
    "CapnProto" provides a separate development package or SDK, be sure it has
    been installed.

  -- Configuring incomplete, errors occurred!
  ```

  with `NO_MODULE`:
  ```
  CMake Error at CMakeLists.txt:16 (find_package):
    Could not find a package configuration file provided by "CapnProto"
    (requested version 0.7) with any of the following names:

      CapnProtoConfig.cmake
      capnproto-config.cmake

    Add the installation prefix of "CapnProto" to CMAKE_PREFIX_PATH or set
    "CapnProto_DIR" to a directory containing one of the above files.  If
    "CapnProto" provides a separate development package or SDK, be sure it has
    been installed.

  -- Configuring incomplete, errors occurred!
  ```

ACKs for top commit:
  ryanofsky:
    Code review ACK 3bee07a. Thanks for the improvement!

Tree-SHA512: 6a0b5568179dc3ffe0a8ac202287dc88a320db016002426c43e33a716191eebf40404af60554244ca601c8c9314b1343d9b190ae69eaa8262648960bf8213089

Author: ryanofsky

CMakeLists.txt

@@ -13,7 +13,7 @@ endif()
 include("cmake/compat_find.cmake")
 
 find_package(Threads REQUIRED)
-find_package(CapnProto 0.7 REQUIRED)
+find_package(CapnProto 0.7 REQUIRED NO_MODULE)
 
 # Check for list-of-pointers memory access bug from Nov 2022
 # https://nvd.nist.gov/vuln/detail/CVE-2022-46149