Make:Allow for extension in tool names.

In some build environments executable programs have a specific file
extension.  The value of BIN_EXT is appended to the relevant tool file
names to allow for this.
The value of BIN_EXT is set, where appropriate, by the build environment
specific make helper (to .exe for Windows build environments).

.gitignore is updated to hide the new (.exe) files.

Change-Id: Icc32f64b750e425265075ad4e0dea18129640b86
diff --git a/make_helpers/windows.mk b/make_helpers/windows.mk
index 92cc8f6..394df3a 100644
--- a/make_helpers/windows.mk
+++ b/make_helpers/windows.mk
@@ -38,9 +38,9 @@
     WINDOWS_MK := $(lastword $(MAKEFILE_LIST))
 
     ECHO_BLANK_LINE := @cmd /c echo.
-
     DIR_DELIM := $(strip \)
-    PATH_SEP := ;
+    BIN_EXT   := .exe
+    PATH_SEP  := ;
 
     # For some Windows native commands there is a problem with the directory delimiter.
     # Make uses / (slash) and the commands expect \ (backslash)