setup_build_environment: Set search path [Linux]

Set the header and library search path for Stdenv.
Fix brew test for Linux, which uses Stdenv.

Library/Homebrew/extend/os/linux/extend/ENV/std.rb

@@ -1,4 +1,17 @@
 module Stdenv
+  def setup_build_environment(formula = nil)
+    generic_setup_build_environment(formula)
+
+    prepend_path "CPATH", HOMEBREW_PREFIX/"include"
+    prepend_path "LIBRARY_PATH", HOMEBREW_PREFIX/"lib"
+    prepend_path "LD_RUN_PATH", HOMEBREW_PREFIX/"lib"
+    return unless formula
+
+    prepend_path "CPATH", formula.include
+    prepend_path "LIBRARY_PATH", formula.lib
+    prepend_path "LD_RUN_PATH", formula.lib
+  end
+
   def libxml2
     append "CPPFLAGS", "-I#{Formula["libxml2"].include/"libxml2"}"
   rescue FormulaUnavailableError