Force cmake packages to use makefiles

Force cmake packages to use the "Unix Makefiles" generator
in case CMAKE_GENERATOR is set in the host environment. This
patch further isolates the buildroot build environment from
the host.

Signed-off-by: Woodrow Douglass <wdouglass@carnegierobotics.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/pkg-cmake.mk

@@ -88,6 +88,7 @@ define $(2)_CONFIGURE_CMDS
 	rm -f CMakeCache.txt && \
 	PATH=$$(BR_PATH) \
 	$$($$(PKG)_CONF_ENV) $$(BR2_CMAKE) $$($$(PKG)_SRCDIR) \
+		-G"Unix MakeFiles" \
 		-DCMAKE_TOOLCHAIN_FILE="$$(HOST_DIR)/share/buildroot/toolchainfile.cmake" \
 		-DCMAKE_INSTALL_PREFIX="/usr" \
 		-DCMAKE_INSTALL_RUNSTATEDIR="/run" \
@@ -118,6 +119,7 @@ define $(2)_CONFIGURE_CMDS
 	PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=1 \
 	PKG_CONFIG_ALLOW_SYSTEM_LIBS=1 \
 	$$($$(PKG)_CONF_ENV) $$(BR2_CMAKE) $$($$(PKG)_SRCDIR) \
+		-G"Unix MakeFiles" \
 		-DCMAKE_INSTALL_SO_NO_EXE=0 \
 		-DCMAKE_FIND_ROOT_PATH="$$(HOST_DIR)" \
 		-DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM="BOTH" \