core: allow having a list of "cmake" candidates

Add the BR2_CMAKE_CANDIDATES variable, containing a list of candidates
to check and use as BR2_CMAKE, if possible.

This allows using "cmake3" on CentOS 7, whose default cmake corresponds
to version 2.8.12. Example:

    $ make BR2_CMAKE_CANDIDATES="cmake cmake3"

Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

support/dependencies/check-host-cmake.mk

@@ -10,9 +10,10 @@
 #
 BR2_CMAKE_VERSION_MIN = 3.1
 
-BR2_CMAKE ?= cmake
-ifeq ($(call suitable-host-package,cmake,\
-	$(BR2_CMAKE_VERSION_MIN) $(BR2_CMAKE)),)
+BR2_CMAKE_CANDIDATES ?= cmake
+BR2_CMAKE ?= $(call suitable-host-package,cmake,\
+	$(BR2_CMAKE_VERSION_MIN) $(BR2_CMAKE_CANDIDATES))
+ifeq ($(BR2_CMAKE),)
 BR2_CMAKE = $(HOST_DIR)/usr/bin/cmake
 BR2_CMAKE_HOST_DEPENDENCY = host-cmake
 endif