Environment variables are configuration-defined.

It was previously inherited, but that behavior was error-prone. This
commit fixes that.

src/context.cr

@@ -74,6 +74,7 @@ class Package::Context
 	property architecture = "x86_64"
 
 	property prefixes = ["/usr", "/", "/usr/weirdos"]
+	property environment = {} of String => String
 
 	def initialize
 		@packaging_backends << Backend::Packaging.new "pkgutils" do |context, package|
@@ -213,7 +214,7 @@ class Package::Context
 	end
 
 	def run(chdir, command, args)
-		Process.run command, args, chdir: chdir, output: Process::Redirect::Inherit, error: Process::Redirect::Inherit
+		Process.run command, args, chdir: chdir, output: Process::Redirect::Inherit, error: Process::Redirect::Inherit, env: @environment
 	end
 
 	def run(command, args)
@@ -263,6 +264,19 @@ class Package::Context
 				@sources_directory = value.as_s
 			when "prefixes"
 				@prefixes = value.as_a_or_s
+			when "environment"
+				value.as_a_or_s.each do |entry|
+					match = entry.split(':').map(
+						&.gsub(/^[ \t]*/, "").gsub(/[ \t]*$/, ""))
+
+					if match.size != 2
+						STDERR.puts "WARNING: misformed environment definition: #{entry}"
+						next
+					end
+
+					key, value = match
+					@environment[key] = value
+				end
 			end
 		end
 	end