point GMPXX_INCLUDE_DIR to locally built gmp (#2030)

* use locally built gmpxx (part of gmp)

* use ignore_package

* reverting to explicitly setting GMP*_INCLUDE_DIR for Windows ❄️

* rm ignore_package(gmpxx); breaks windows

cmake/recipes/external/cgal.cmake

@@ -34,8 +34,10 @@ function(cgal_import_target)
     include(boost)
 
     ignore_package(GMP 5.0.1)
-    set(GMP_INCLUDE_DIR "")
+    set(GMP_INCLUDE_DIR ${gmp_INCLUDE_DIR})
     set(GMP_LIBRARIES gmp::gmp)
+    set(GMPXX_INCLUDE_DIR ${GMP_INCLUDE_DIR})
+    set(GMPXX_LIBRARIES ${GMP_LIBRARIES})
 
     ignore_package(MPFR 3.0.0)
     set(MPFR_INCLUDE_DIR "")

cmake/recipes/external/gmp.cmake

@@ -17,7 +17,10 @@ else()
   set(prefix ${FETCHCONTENT_BASE_DIR}/gmp)
   set(gmp_INSTALL ${prefix}/install)
   set(gmp_LIB_DIR ${gmp_INSTALL}/lib)
-  set(gmp_LIBRARY ${gmp_LIB_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}gmp${CMAKE_STATIC_LIBRARY_SUFFIX})
+  set(gmp_LIBRARY 
+    ${gmp_LIB_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}gmp${CMAKE_STATIC_LIBRARY_SUFFIX}
+    ${gmp_LIB_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}gmpxx${CMAKE_STATIC_LIBRARY_SUFFIX}
+    )
   set(gmp_INCLUDE_DIR ${gmp_INSTALL}/include)
 
   # Try to use CONFIGURE_HANDLED_BY_BUILD ON to avoid constantly reconfiguring