HV: make: append dependency checking targets to a given variable

The current implementation of the check_dep_* macros always append the
prerequisite checking target to BUILD_DEPS, but there are some cases when some
prerequisites are only necessary for some specific targets instead of general
builds.

This patch adds a second parameter to the check_dep_* macros specifying which
variable the generated target should be appended to.

Signed-off-by: Junjie Mao <junjie.mao@intel.com>
Acked-by: Anthony Xu <anthony.xu@intel.com>
Acked-by: Geoffroy VanCutsem <geoffroy.vancutsem@intel.com>

scripts/deps.mk

@@ -1,8 +1,10 @@
-# check the existence of a specific executable
-# usage: check_dep_exec <executable name>
+# usage: check_dep_exec <executable name> <variable>
+#
+# Create a target that checks the existence of the specified executable, and
+# append that target to the given variable.
 define check_dep_exec =
-BUILD_DEPS += check_$(1)
-check_$(1):
+$(2) += check_exec_$(1)
+check_exec_$(1):
 	@if ! which $(1) > /dev/null; then   \
 	     echo "******** Missing prerequisite tool ********"; \
 	     echo "Cannot find executable *$(1)*"; \
@@ -12,11 +14,14 @@ check_$(1):
 	 fi
 endef
 
-# check the existence of a specific python library
-# usage: check_dep_pylib <library name>
+# usage: check_dep_pylib <library name> <variable>
+#
+# Create a target that checks the existence of the specified python library, and
+# append that target to the given variable. The default python version (which
+# can be either 2.x or 3.x) is used.
 define check_dep_pylib =
-BUILD_DEPS += check_$(1)
-check_$(1):
+$(2) += check_pylib_$(1)
+check_pylib_$(1):
 	@if ! pip list 2>/dev/null | grep $(1) > /dev/null 2>&1; then   \
 	     echo "******** Missing prerequisite tool ********"; \
 	     echo "The python library *$(1)* is not installed"; \