Handle python2 not being installed, but python3 being present

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

PyIlmBase/CMakeLists.txt

@@ -45,11 +45,11 @@ endif()
 find_package(Python2 COMPONENTS Interpreter Development)
 find_package(Python3 COMPONENTS Interpreter Development)
 if(TARGET Python2::Python AND TARGET Python3::Python)
-  message(NOTICE ": Found Python ${Python2_VERSION} and ${Python3_VERSION}")
+  message(STATUS ": Found Python ${Python2_VERSION} and ${Python3_VERSION}")
 elseif(TARGET Python2::Python)
-  message(NOTICE ": Found Python ${Python2_VERSION}")
+  message(STATUS ": Found Python ${Python2_VERSION}")
 elseif(TARGET Python3::Python)
-  message(NOTICE ": Found Python ${Python3_VERSION}")
+  message(STATUS ": Found Python ${Python3_VERSION}")
 else()
   message(WARNING ": Unable to find python development libraries for python 2 or 3")
   return()
@@ -125,9 +125,15 @@ find_package(Boost OPTIONAL_COMPONENTS
 set(_pyilmbase_have_perver_boost)
 if(PYILMBASE_BOOST_PY2_COMPONENT)
   string(TOUPPER ${PYILMBASE_BOOST_PY2_COMPONENT} PYILMBASE_PY2_UPPER)
+else()
+  set(PYILMBASE_BOOST_PY2_COMPONENT python2x_NOTFOUND)
+  set(PYILMBASE_PY2_UPPER PYTHON2X_NOTFOUND)
 endif()
 if(PYILMBASE_BOOST_PY3_COMPONENT)
   string(TOUPPER ${PYILMBASE_BOOST_PY3_COMPONENT} PYILMBASE_PY3_UPPER)
+else()
+  set(PYILMBASE_BOOST_PY3_COMPONENT python3x_NOTFOUND)
+  set(PYILMBASE_PY3_UPPER PYTHON3X_NOTFOUND)
 endif()
 if(Boost_PYTHON2_FOUND OR Boost_${PYILMBASE_PY2_UPPER}_FOUND)
   set(_pyilmbase_have_perver_boost TRUE)
@@ -167,9 +173,9 @@ else()
     return()
   endif()
 endif()
-set(PYILMBASE_PY2_UPPER)
-set(PYILMBASE_PY3_UPPER)
-set(_pyilmbase_have_perver_boost)
+unset(PYILMBASE_PY2_UPPER)
+unset(PYILMBASE_PY3_UPPER)
+unset(_pyilmbase_have_perver_boost)
 
 # unfortunately, we can't use the boost numpy stuff, as that requires a
 # version of boost that is newer than is mandated by many active versions