cmake: use pkg-config to discover docopt

The upstream project provides a CMake file which attempts to import both
static and shared libraries. This is a problem on any reasonable
distribution because Nobody Ships Static Libraries Anymore (for
reasonable reasons). So we have distros shipping CMake files from
upstream which are broken because distros actively remove the static
library from their packaging.

This was not caught by the CI because `Depends-on` was not typed
properly , and therefore Zuul would feed oldish prebuilt dependencies
which still included the custom-built docopt library in both static and
shared versions. We need a linter for commit footers :p.

Fixes: Ib246d39f975c00bc6489f683f1f21f34cc808201
Fixes: c64c42a CI: use system docopt-cpp
Bug: docopt/docopt.cpp#134
Change-Id: Ia50595b36cfe233fd67a5153ff804d77a0c77b94

CMakeLists.txt

@@ -21,11 +21,11 @@ prepare_git_version(SYSREPO_IETF_ALARMS_VERSION "0.0")
 find_package(Doxygen)
 option(WITH_DOCS "Create and install internal documentation (needs Doxygen)" ${DOXYGEN_FOUND})
 
-find_package(docopt REQUIRED)
 find_package(spdlog REQUIRED)
 find_package(PkgConfig REQUIRED)
 find_package(date REQUIRED)
 
+pkg_check_modules(DOCOPT REQUIRED IMPORTED_TARGET docopt)
 pkg_check_modules(SYSREPO REQUIRED IMPORTED_TARGET sysrepo-cpp>=1.1.0 sysrepo)
 pkg_check_modules(LIBYANG REQUIRED IMPORTED_TARGET libyang-cpp>=1.1.0)
 pkg_check_modules(SYSTEMD REQUIRED IMPORTED_TARGET libsystemd)
@@ -79,7 +79,7 @@ target_link_libraries(alarms PUBLIC alarms-utils)
 
 add_executable(sysrepo-ietf-alarmsd src/main.cpp)
 add_dependencies(sysrepo-ietf-alarmsd target-SYSREPO_IETF_ALARMS_VERSION)
-target_link_libraries(sysrepo-ietf-alarmsd PUBLIC alarms docopt PRIVATE PkgConfig::SYSTEMD)
+target_link_libraries(sysrepo-ietf-alarmsd PUBLIC alarms PkgConfig::DOCOPT PRIVATE PkgConfig::SYSTEMD)
 
 # Testing
 include(CTest)