Identify the basic issues with ExtProject_Target

Three remaining issues surfaced with the RPATH setting - two minor, one
trickier.

Minor #1 - Itcl and Itk didn't have the RPATH flag set in their target
definitions (fixed).

Minor #2 - 3rd party binaries RPATHs don't match those produced by the
main CMake build - using bin instead of lib (investigating).

More significant is the behavior of CMake's RPATH_CHANGE - it is
correctly setting the final path, but it is not clearing the build dir
path.  So far I've not found a way to make the available commands in
CMake do the job, so I'm falling back on a solution similar to that
necessary on Apple and using the chrpath utility.  The code in this
commit works if a system chrpath is present - we'll need to bundle a
version in misc/tools to make sure we have the capabilities we need
reliably.  (chrpath is GPL, so we can't install it or use it as anything
except a build tool - unfortunately I've not found a BSD/MIT licensed
tool for this type of rpath work...)

src/other/ext/CMake/ExternalProject_Target.cmake

@@ -249,6 +249,7 @@ endfunction(ET_Origin_Path)
 # /usr/bin/baz -> bin/baz
 # /usr/bin/mypkg/baz -> bin/mypkg/baz
 #
+find_program(CHRPATH_EXEC chrpath)
 function(ET_RPath OFILE)
   get_filename_component(OFPATH "${OFILE}" DIRECTORY)
   get_filename_component(RRPATH "${CMAKE_INSTALL_PREFIX}/${OFPATH}" REALPATH)
@@ -272,7 +273,16 @@ function(ET_RPath OFILE)
     execute_process(COMMAND install_name_tool -delete_rpath \"${CMAKE_BUILD_RPATH}\" \"\${WPATH}\")
     execute_process(COMMAND install_name_tool -add_rpath \"${NEW_RPATH}\" \"\${WPATH}\")
     ")
-  else (APPLE)
+  elseif (CHRPATH_EXEC)
+    # Looks like CMake's built in RPATH logic isn't quite enough for our
+    # purposes here - it leaves the build RPATH in place even after assigning
+    # the new path.
+    # TODO Need to bundle chrpath so we can reliably do this...
+    install(CODE "
+    set(WPATH \"\$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/${OFILE}\")
+    execute_process(COMMAND chrpath -r \"${NEW_RPATH}\" \"\${WPATH}\")
+    ")
+  else ()
     install(CODE "
     file(RPATH_CHANGE
       FILE \"\$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/${OFILE}\"

src/other/ext/itcl.cmake

@@ -134,6 +134,7 @@ if (BRLCAD_ENABLE_TCL)
     ExternalProject_Target(SHARED itcl ITCL_BLD ${ITCL_INSTDIR}
       itcl${ITCL_VERSION}/${ITCL_BASENAME}${CMAKE_SHARED_LIBRARY_SUFFIX}
       SUBDIR  itcl${ITCL_VERSION}
+      RPATH
       )
 
     ExternalProject_Target(STATIC itclstub ITCL_BLD ${ITCL_INSTDIR}

src/other/ext/itk.cmake

@@ -107,6 +107,7 @@ if (BRLCAD_ENABLE_TK)
     ExternalProject_Target(SHARED itk ITK_BLD ${ITK_INSTDIR}
       itk${ITK_VERSION}/${ITK_BASENAME}${CMAKE_SHARED_LIBRARY_SUFFIX}
       SUBDIR itk${ITK_VERSION}
+      RPATH
       )
 
     ExternalProject_ByProducts(itk ITK_BLD ${ITK_INSTDIR} ${INCLUDE_DIR}