Merge pull request #121 from kost/fix-cmake-python

pytrellis should be target if BUILD_PYTHON exists

libtrellis/CMakeLists.txt

diff --git a/libtrellis/CMakeLists.txt b/libtrellis/CMakeLists.txt
index b19e727..10fd498 100644
--- a/libtrellis/CMakeLists.txt
+++ b/libtrellis/CMakeLists.txt
@@ -33,6 +33,7 @@
 
 if (BUILD_PYTHON)
     find_package(PythonLibs 3.5 REQUIRED)
+    set(PythonInstallTarget "pytrellis")
 endif()
 
 find_package(Boost REQUIRED COMPONENTS ${boost_libs})
@@ -174,7 +175,7 @@
 setup_rpath(ecpmulti)
 
 if (BUILD_SHARED)
-    install(TARGETS trellis ecpbram ecppack ecppll ecpunpack ecpmulti pytrellis
+    install(TARGETS trellis ecpbram ecppack ecppll ecpunpack ecpmulti ${PythonInstallTarget}
             LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}/trellis
             RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})
 else()