make: create target directory if symlinked

Handles the case where the build directory is a symbolic link
to another directory and the target directory does not exist.

This allows seamlessly building lone in RAM using tmpfs by simply
creating a symbolic link to a non-existent directory of a mounted
RAM file system.

  ln -s /tmp/lone/build
  ln -s /run/user/1000/lone/build

GNUmakefile

@@ -40,7 +40,8 @@ source_to_test = $(patsubst $(directories.source.tests)/%.c,$(directories.build.
 
 ARCH := $(TARGET)
 
-directories.build := build/$(ARCH)
+directories.build.root := build
+directories.build := $(directories.build.root)/$(ARCH)
 directories.build.tools := $(directories.build)/tools
 directories.build.tests := $(directories.build)/tests
 directories.build.objects := $(directories.build)/objects
@@ -156,6 +157,7 @@ test: tests lone tools
 
 targets.phony += directories
 directories:
+	scripts/create-symlinked-directory.bash $(directories.build.root)
 	mkdir -p $(sort $(directories.create))
 
 .PHONY: $(targets.phony)

scripts/create-symlinked-directory.bash

@@ -0,0 +1,9 @@
+#!/usr/bin/bash
+
+directory="${1}"
+linked="$(readlink "${directory}")"
+result="${?}"
+
+if [[ "${result}" -eq 0 && ! -d "${linked}" ]]; then
+  mkdir -p "${linked}"
+fi