Support product variables

Allow modules to vary their properties based on product variables.
For now, DEVICE_USES_LOGD, DEVICE_USES_JEMALLOC, and DEVICE_USES_DLMALLOC,
and BOARD_MALLOC_ALIGNMENT are supported.

Product variables can provide a value (only bool and int supported for
now), and if any of the product variable properties contains a "%d"
then Sprintf will be called with the property value as the format
and the product variable value convert to an int as the only argument.

For example:

    product_variables: {
        dlmalloc_alignment: {
            cflags: ["-DMALLOC_ALIGNMENT=%d"],
        },
    },

will cause -DMALLOC_ALIGNMENT=16 to be added to any top level
properties called "cflags".

Change-Id: I74882a6ab4914d3e222f8d06cfac371b7b829ae5

androidbp/cmd/soong.go

@@ -172,3 +172,10 @@ var targetToHostModuleRule = map[string]string{
 	"BUILD_NATIVE_TEST":    "BUILD_HOST_NATIVE_TEST",
 	"BUILD_JAVA_LIBRARY":   "BUILD_HOST_JAVA_LIBRARY",
 }
+
+var productVariableConditionals = map[string]struct{conditional, value string}{
+	"device_uses_jemalloc": {"ifneq ($(MALLOC_IMPL),dlmalloc)", ""},
+	"device_uses_dlmalloc": {"ifeq ($(MALLOC_IMPL),dlmalloc)", ""},
+	"device_uses_logd":     {"ifneq ($(TARGET_USES_LOGD),false)", ""},
+	"dlmalloc_alignment":   {"ifdef DLMALLOC_ALIGNMENT", "$(DLMALLOC_ALIGNMENT)"},
+}