autotools.bbclass: mkdir ${B} -> mkdir -p ${B}

${B} is the default cwd of tasks, so there might be race issues such as:
| mkdir: cannot create directory `${B}': File exists
[snip]
NOTE: recipe perf-1.0-r9: task do_configure: Failed

(From OE-Core rev: 4c02a30f084408d0a6a5149937ef74520f8346dc)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/autotools.bbclass

@@ -105,7 +105,7 @@ autotools_preconfigure() {
 			if [ "${S}" != "${B}" ]; then
 				echo "Previously configured separate build directory detected, cleaning ${B}"
 				rm -rf ${B}
-				mkdir ${B}
+				mkdir -p ${B}
 			else
 				# At least remove the .la files since automake won't automatically
 				# regenerate them even if CFLAGS/LDFLAGS are different