faster to compile.

A small selection of packages was tested going from:

Executed in  696.30 secs   fish           external
   usr time   82.98 mins  395.00 micros   82.98 mins
   sys time    9.02 mins    0.00 micros    9.02 mins

to:

Executed in  592.20 secs   fish           external
   usr time   84.84 mins  361.00 micros   84.84 mins
   sys time    8.85 mins   57.00 micros    8.85 mins

Tested by running make -j 12 and wiping staging/build_dir/target_x

Signed-off-by: Rosen Penev <rosenp@gmail.com>

This removes lines that set PKG_BUILD_DIR when the set value is no
different from the default value.

Specifically, the line is removed if the assigned value is:

* $(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_NAME)-$(PKG_VERSION)

  The default PKG_BUILD_DIR was updated[1] to incorporate BUILD_VARIANT
  if it is set, so now this is identical to the default value.

* $(BUILD_DIR)/$(PKG_NAME)-$(BUILD_VARIANT)/$(PKG_SOURCE_SUBDIR)

  if PKG_SOURCE_SUBDIR is set to $(PKG_NAME)-$(PKG_VERSION), making it
  the same as the previous case

* $(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)

  This is the same as the default PKG_BUILD_DIR when there is no
  BUILD_VARIANT.

* $(BUILD_DIR)/[name]-$(PKG_VERSION)

  where [name] is a string that is identical to PKG_NAME

[1]: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=e545fac8d968864a965edb9e50c6f90940b0a6c9

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

fix Makefile chmod (644)
replace MD5SUM with HASH
add PKG_MIRROR_HASH when PKG_SOURCE_PROTO:=git

(PKG_SOURCE_PROTO:=svn tarballs are not reproducible for now)

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

LUA_MATH_LIBRARY=m is added as lua-cjson fails to detect Lua in the host
build without it.

Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>

Signed-off-by: Dirk Chang <dirk@kooiot.com>

Signed-off-by: Dirk Chang <dirk@kooiot.com>