cmake: Use LIB_INSTALL_DIR instead of hardcoding lib destination (#78)

The comon practice in cmake to allow to specify the libdir is
using the LIB_INSTALL_DIR variable. The main use case of that
variable is setting /usr/lib64 as the destination dir for
libraries which is a common pattern in many Linux distributions.

CMakeLists.txt

@@ -86,6 +86,13 @@ if (NOT BUILD_SHARED_LIBS AND NOT BUILD_STATIC_LIBS)
     message(FATAL_ERROR "One or both of BUILD_SHARED_LIBS or BUILD_STATIC_LIBS must be set to ON to build")
 endif()
 
+# ==============================================================================
+# Set up libdir
+
+if (NOT DEFINED LIB_INSTALL_DIR)
+    set(LIB_INSTALL_DIR ${CMAKE_INSTALL_PREFIX}/lib)
+endif()
+
 # ==============================================================================
 # Set up generated header files config.h and version.h
 
@@ -127,8 +134,8 @@ if (BUILD_SHARED_LIBS)
   set_target_properties(opentracing PROPERTIES VERSION ${OPENTRACING_VERSION_STRING}
                                              SOVERSION ${OPENTRACING_VERSION_MAJOR})
   install(TARGETS opentracing EXPORT OpenTracingTargets
-          LIBRARY DESTINATION lib
-          ARCHIVE DESTINATION lib)
+          LIBRARY DESTINATION ${LIB_INSTALL_DIR}
+          ARCHIVE DESTINATION ${LIB_INSTALL_DIR})
   if (CLANG_TIDY_EXE)
     set_target_properties(opentracing PROPERTIES
                                     CXX_CLANG_TIDY "${DO_CLANG_TIDY}")
@@ -141,7 +148,7 @@ if (BUILD_STATIC_LIBS)
   set_target_properties(opentracing-static PROPERTIES OUTPUT_NAME opentracing)
   target_include_directories(opentracing-static INTERFACE "$<INSTALL_INTERFACE:include/>")
   install(TARGETS opentracing-static EXPORT OpenTracingTargets
-          ARCHIVE DESTINATION lib)
+	  ARCHIVE DESTINATION ${LIB_INSTALL_DIR})
 endif()
 
 
@@ -172,7 +179,7 @@ export(EXPORT OpenTracingTargets
 configure_file(cmake/OpenTracingConfig.cmake
     "${CMAKE_CURRENT_BINARY_DIR}/OpenTracingConfig.cmake"
     COPYONLY)
-set(ConfigPackageLocation lib/cmake/OpenTracing)
+set(ConfigPackageLocation ${LIB_INSTALL_DIR}/cmake/OpenTracing)
 install(EXPORT OpenTracingTargets
     FILE OpenTracingTargets.cmake
     NAMESPACE OpenTracing::

mocktracer/CMakeLists.txt

@@ -17,8 +17,8 @@ if (BUILD_SHARED_LIBS)
                                                SOVERSION ${OPENTRACING_VERSION_MAJOR})
   target_link_libraries(opentracing_mocktracer opentracing)
   install(TARGETS opentracing_mocktracer EXPORT OpenTracingTargets
-          LIBRARY DESTINATION lib
-          ARCHIVE DESTINATION lib)
+          LIBRARY DESTINATION ${LIB_INSTALL_DIR}
+          ARCHIVE DESTINATION ${LIB_INSTALL_DIR})
 endif()
 
 if (BUILD_STATIC_LIBS)
@@ -27,7 +27,7 @@ if (BUILD_STATIC_LIBS)
   target_include_directories(opentracing_mocktracer-static INTERFACE "$<INSTALL_INTERFACE:include/>")
   target_link_libraries(opentracing_mocktracer-static opentracing-static)
   install(TARGETS opentracing_mocktracer-static EXPORT OpenTracingTargets
-          ARCHIVE DESTINATION lib)
+	  ARCHIVE DESTINATION ${LIB_INSTALL_DIR})
 endif()
 
 install(DIRECTORY include/opentracing DESTINATION include