+Avoid opportunistic linkage against libdb and libicu.
+
+diff -u -r ../libical-3.0.1/CMakeLists.txt ./CMakeLists.txt
+--- ../libical-3.0.1/CMakeLists.txt 2017-11-19 14:32:53.000000000 +0000
++++ ./CMakeLists.txt 2017-12-08 23:54:59.745527096 +0000
+@@ -154,47 +154,6 @@
+ set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_LIB64_PATHS True)
+ endif()
+
+-# libicu is highly recommended for RSCALE support
+-# libicu can be found at http://www.icu-project.org
+-# RSCALE info at http://tools.ietf.org/html/rfc7529
+-find_package(ICU)
+-set_package_properties(ICU PROPERTIES
+- TYPE RECOMMENDED
+- PURPOSE "For RSCALE (RFC7529) support"
+-)
+-add_feature_info(
+- "RSCALE support (RFC7529)"
+- ICU_FOUND
+- "build in RSCALE support"
+-)
+-if(ICU_FOUND)
+- set(REQUIRES_PRIVATE_ICU "Requires.private: icu-i18n") #for libical.pc
+- set(HAVE_LIBICU 1)
+- if(ICU_MAJOR_VERSION VERSION_GREATER 50)
+- set(HAVE_ICU_DANGI TRUE)
+- else()
+- set(HAVE_ICU_DANGI FALSE)
+- endif()
+-endif()
+-if(ICU_I18N_FOUND)
+- set(HAVE_LIBICU_I18N 1)
+-endif()
+-
+-# compile in Berkeley DB support
+-find_package(BDB)
+-set_package_properties(BDB PROPERTIES
+- TYPE OPTIONAL
+- PURPOSE "For Berkeley DB storage support"
+-)
+-add_feature_info(
+- "Berkeley DB storage support"
+- BDB_FOUND
+- "build in support for Berkeley DB storage"
+-)
+-if(BDB_FOUND)
+- set(HAVE_BDB True)
+-endif()
+-
+ # MSVC specific definitions
+ if(WIN32)
+ if(MSVC)