treewide: add ORIG_PATH variable

Add a variable that stores the original value of $PATH
in the host system's shell, before Make alters it.

This can be useful for when it is necessary
to ignore symlinks and programs made by the build system.

Define this new variable before all instances of
'export PATH:=' or similar.

Signed-off-by: Michael Pratt <mcpratt@pm.me>

rules.mk

@@ -227,6 +227,7 @@ else
   endif
 endif
 
+export ORIG_PATH:=$(if $(ORIG_PATH),$(ORIG_PATH),$(PATH))
 export PATH:=$(TARGET_PATH)
 export STAGING_DIR STAGING_DIR_HOST STAGING_DIR_HOSTPKG
 export SH_FUNC:=. $(INCLUDE_DIR)/shell.sh;