Makefile.autotools.in: honor CONFIG_SHELL and TAR.

  Don't use recursively expanded definition
  (Use ':=' instead of '=')

package/Makefile.autotools.in

@@ -125,7 +125,7 @@ TAR ?= tar
 #	ACLOCAL="$(ACLOCAL)"
 
 # Automatically detect tar --strip-path/components option
-TAR_STRIP_COMPONENTS = $(shell tar --help | grep strip-path > /dev/null ; if test $$? = 0 ; then echo '--strip-path' ; else echo '--strip-components' ; fi)
+TAR_STRIP_COMPONENTS := $(shell $(CONFIG_SHELL) -c '$(TAR) --help | grep strip-path > /dev/null ; if test $$? = 0 ; then echo '--strip-path' ; else echo '--strip-components' ; fi')
 
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 # Implicit targets -- produce a stamp file for each step of a package build