Fix pkg-config files when using the CMake build system.

Upstream bug report:
https://github.com/openexr/openexr/issues/567

diff --git a/IlmBase/config/CMakeLists.txt b/IlmBase/config/CMakeLists.txt
index 508176a..9e6ab91 100644
--- a/IlmBase/config/CMakeLists.txt
+++ b/IlmBase/config/CMakeLists.txt
@@ -71,9 +71,9 @@ if(ILMBASE_INSTALL_PKG_CONFIG)
   # use a helper function to avoid variable pollution, but pretty simple
   function(ilmbase_pkg_config_help pcinfile)
     set(prefix ${CMAKE_INSTALL_PREFIX})
-    set(exec_prefix ${CMAKE_INSTALL_BINDIR})
-    set(libdir ${CMAKE_INSTALL_LIBDIR})
-    set(includedir ${CMAKE_INSTALL_INCLUDEDIR})
+    set(exec_prefix ${CMAKE_INSTALL_FULL_BINDIR})
+    set(libdir ${CMAKE_INSTALL_FULL_LIBDIR})
+    set(includedir ${CMAKE_INSTALL_FULL_INCLUDEDIR})
     set(LIB_SUFFIX_DASH ${ILMBASE_LIB_SUFFIX})
     if(TARGET Threads::Threads)
       # hrm, can't use properties as they end up as generator expressions
diff --git a/OpenEXR/config/CMakeLists.txt b/OpenEXR/config/CMakeLists.txt
index 1ef829a..b8dc141 100644
--- a/OpenEXR/config/CMakeLists.txt
+++ b/OpenEXR/config/CMakeLists.txt
@@ -72,9 +72,9 @@ if(OPENEXR_INSTALL_PKG_CONFIG)
   # use a helper function to avoid variable pollution, but pretty simple
   function(openexr_pkg_config_help pcinfile)
     set(prefix ${CMAKE_INSTALL_PREFIX})
-    set(exec_prefix ${CMAKE_INSTALL_BINDIR})
-    set(libdir ${CMAKE_INSTALL_LIBDIR})
-    set(includedir ${CMAKE_INSTALL_INCLUDEDIR})
+    set(exec_prefix ${CMAKE_INSTALL_FULL_BINDIR})
+    set(libdir ${CMAKE_INSTALL_FULL_LIBDIR})
+    set(includedir ${CMAKE_INSTALL_FULL_INCLUDEDIR})
     set(LIB_SUFFIX_DASH ${OPENEXR_LIB_SUFFIX})
     if(TARGET Threads::Threads)
       # hrm, can't use properties as they end up as generator expressions