minor fixes for UHDConfig.cmake on windows

[guruofquality]

Not to get too pedantic, but the following changes streamlined the ability of a dependency project to find UHD automatically on a windows system with find_package(UHD CONFIG):

• Install the file to $prefix/cmake/UHDConfig.cmake (windows cmake has different search paths which can be read about here: https://www.cmake.org/cmake/help/v3.0/command/find_package.html)
• The UHD_INCLUDE_HINTS and UHD_LIBDIR_HINTS variables can be set automatically relative to UHDConfig.cmake using ${CMAKE_CURRENT_LIST_DIR}, this way they are always found.

diff --git a/host/cmake/Modules/UHDConfig.cmake.in b/host/cmake/Modules/UHDConfig.cmake.in
index 78f0170..593a699 100644
--- a/host/cmake/Modules/UHDConfig.cmake.in
+++ b/host/cmake/Modules/UHDConfig.cmake.in
@@ -40,6 +40,10 @@ SET(UHD_INCLUDE_HINTS)
 SET(UHD_LIBDIR_HINTS)
 SET(UHD_DIR $ENV{UHD_DIR})

+IF(NOT UHD_DIR AND WIN32)
+    get_filename_component(UHD_DIR "${CMAKE_CURRENT_LIST_DIR}/.." ABSOLUTE)
+ENDIF()
+
 IF(UHD_DIR)
     LIST(APPEND UHD_INCLUDE_HINTS ${UHD_DIR}/include)
     LIST(APPEND UHD_LIBDIR_HINTS ${UHD_DIR}/lib)