builddeb: avoid invoking sub-shells where possible

The commands surrounded by ( ... ) is run in a sub-shell, but you do
not have to spawn a sub-shell for every single line.

Use just one ( ... ) for creating debian/hdrsrcfiles.

For tar, use -C option instead.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/package/builddeb

@@ -165,21 +165,30 @@ EOF
 done
 
 # Build kernel header package
-(cd $srctree; find . arch/$SRCARCH -maxdepth 1 -name Makefile\*) > debian/hdrsrcfiles
-(cd $srctree; find include scripts -type f -o -type l) >> debian/hdrsrcfiles
-(cd $srctree; find arch/$SRCARCH -name module.lds -o -name Kbuild.platforms -o -name Platform) >> debian/hdrsrcfiles
-(cd $srctree; find $(find arch/$SRCARCH -name include -o -name scripts -type d) -type f) >> debian/hdrsrcfiles
-if is_enabled CONFIG_STACK_VALIDATION; then
-	echo tools/objtool/objtool >> debian/hdrobjfiles
-fi
-find arch/$SRCARCH/include Module.symvers include scripts -type f >> debian/hdrobjfiles
-if is_enabled CONFIG_GCC_PLUGINS; then
-	find scripts/gcc-plugins -name \*.so >> debian/hdrobjfiles
-fi
+(
+	cd $srctree
+	find . arch/$SRCARCH -maxdepth 1 -name Makefile\*
+	find include scripts -type f -o -type l
+	find arch/$SRCARCH -name module.lds -o -name Kbuild.platforms -o -name Platform
+	find $(find arch/$SRCARCH -name include -o -name scripts -type d) -type f
+) > debian/hdrsrcfiles
+
+{
+	if is_enabled CONFIG_STACK_VALIDATION; then
+		echo tools/objtool/objtool
+	fi
+
+	find arch/$SRCARCH/include Module.symvers include scripts -type f
+
+	if is_enabled CONFIG_GCC_PLUGINS; then
+		find scripts/gcc-plugins -name \*.so
+	fi
+} > debian/hdrobjfiles
+
 destdir=$kernel_headers_dir/usr/src/linux-headers-$version
 mkdir -p "$destdir"
-(cd $srctree; tar -c -f - -T -) < debian/hdrsrcfiles | (cd $destdir; tar -xf -)
-tar -c -f - -T - < debian/hdrobjfiles | (cd $destdir; tar -xf -)
+tar -c -f - -C $srctree -T debian/hdrsrcfiles | tar -xf - -C $destdir
+tar -c -f - -T debian/hdrobjfiles | tar -xf - -C $destdir
 cp $KCONFIG_CONFIG $destdir/.config # copy .config manually to be where it's expected to be
 ln -sf "/usr/src/linux-headers-$version" "$kernel_headers_dir/lib/modules/$version/build"
 rm -f debian/hdrsrcfiles debian/hdrobjfiles