Build: add propper build configuration concept

Makefile.conf

@@ -3,7 +3,24 @@
 # This file may be used under the terms of the GNU General Public License version 3
 # see LICENSE.txt
 
-HERE:=$(dir $(lastword $(MAKEFILE_LIST)))
+# BUILD_CONF must be specified relative to the repo root or must be an absolute path
+# BUILD_CONF defaults to ./build.conf
+REPO_ROOT_REL:=$(dir $(lastword $(MAKEFILE_LIST)))
+ifndef BUILD_CONF
+    BUILD_CONF=$(REPO_ROOT_REL)/build.conf
+    -include $(BUILD_CONF)
+else
+    BUILD_CONF_EFF=$(BUILD_CONF)
+    ifeq ($(dir $(BUILD_CONF)),./)
+        BUILD_CONF_EFF=$(REPO_ROOT_REL)/$(BUILD_CONF)
+    endif
+    ifeq ($(wildcard $(BUILD_CONF_EFF)),)
+        $(info BUILD_CONF must be specified relative to the repo root or must be an absolute path)
+        $(error file specified using BUILD_CONF ($(BUILD_CONF)) not found)
+    endif
+    include $(BUILD_CONF_EFF)
+endif
+
 
 TARGET=libpEpAdapter.a
 
@@ -12,9 +29,6 @@ TARGET=libpEpAdapter.a
 DEBUG=1
 PREFIX?=$(HOME)
 
-# Overrides
--include $(HERE)build.conf
-
 # Constants
 CXXFLAGS+=-std=c++11 -fPIC
 CXXFLAGS+=-Wall -pedantic-errors -Wno-unused-parameter -Wno-reorder-ctor

README.md

@@ -3,7 +3,9 @@
 
 ## Build Configuration
 
-The build configuration file is called `build.conf`.
+The build configuration file is called `build.conf` or can be specified (relative to repo root) using 
+the env var `BUILD_CONF`.
+
 Use the file `build.conf.example` as a template.
 
 ```bash