Fix configure tests to play nice with GCC 4.6

As of GCC 4.6, specific kernel 2.6.32 header files do not compile
cleanly without warnings. One specific example of this is the
arch/x86/include/asm/percpu.h file. Thus, a few of the configure tests
were getting hung up on this and the '-Wno-unsued-but-set-variables'
compile option had to be introduced.

Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes openzfs#459

config/kernel-bdev-block-device-operations.m4

@@ -3,6 +3,8 @@ dnl # 2.6.x API change
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BDEV_BLOCK_DEVICE_OPERATIONS], [
 	AC_MSG_CHECKING([block device operation prototypes])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -30,4 +32,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BDEV_BLOCK_DEVICE_OPERATIONS], [
 	],[
 		AC_MSG_RESULT(struct inode)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-bdev-logical-size.m4

@@ -7,6 +7,8 @@ dnl # it explicit.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BDEV_LOGICAL_BLOCK_SIZE], [
 	AC_MSG_CHECKING([whether bdev_logical_block_size() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -19,4 +21,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BDEV_LOGICAL_BLOCK_SIZE], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-blk-end-request.m4

@@ -5,6 +5,8 @@ dnl # changed in 2.6.31 so it may be used by non-GPL modules.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BLK_END_REQUEST], [
 	AC_MSG_CHECKING([whether blk_end_request() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -34,4 +36,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_END_REQUEST], [
 		AC_DEFINE(HAVE_BLK_END_REQUEST_GPL_ONLY, 1,
 		          [blk_end_request() is GPL-only])
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-blk-fetch-request.m4

@@ -7,6 +7,8 @@ dnl # next available request and removed it from the request queue.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BLK_FETCH_REQUEST], [
 	AC_MSG_CHECKING([whether blk_fetch_request() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -19,4 +21,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_FETCH_REQUEST], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-blk-requeue-request.m4

@@ -6,6 +6,8 @@ dnl # blk_requeue_request() function.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BLK_REQUEUE_REQUEST], [
 	AC_MSG_CHECKING([whether blk_requeue_request() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -19,4 +21,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_REQUEUE_REQUEST], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-blk-rq-bytes.m4

@@ -6,6 +6,8 @@ dnl blk_rq_bytes() helper was changed to a static inline which we can use.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BLK_RQ_BYTES], [
 	AC_MSG_CHECKING([whether blk_rq_bytes() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -35,4 +37,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_RQ_BYTES], [
 		AC_DEFINE(HAVE_BLK_RQ_BYTES_GPL_ONLY, 1,
 		          [blk_rq_bytes() is GPL-only])
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-blk-rq-pos.m4

@@ -3,6 +3,8 @@ dnl # 2.6.31 API change
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BLK_RQ_POS], [
 	AC_MSG_CHECKING([whether blk_rq_pos() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -15,4 +17,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_RQ_POS], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-blk-rq-sectors.m4

@@ -3,6 +3,8 @@ dnl # 2.6.31 API change
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_BLK_RQ_SECTORS], [
 	AC_MSG_CHECKING([whether blk_rq_sectors() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -15,4 +17,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_RQ_SECTORS], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-get-disk-ro.m4

@@ -3,6 +3,8 @@ dnl # 2.6.x API change
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_GET_DISK_RO], [
 	AC_MSG_CHECKING([whether get_disk_ro() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -15,4 +17,5 @@ AC_DEFUN([ZFS_AC_KERNEL_GET_DISK_RO], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-rq-for-each_segment.m4

@@ -3,6 +3,8 @@ dnl # 2.6.x API change
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_RQ_FOR_EACH_SEGMENT], [
 	AC_MSG_CHECKING([whether rq_for_each_segment() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -17,4 +19,5 @@ AC_DEFUN([ZFS_AC_KERNEL_RQ_FOR_EACH_SEGMENT], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])

config/kernel-rq-is_sync.m4

@@ -3,6 +3,8 @@ dnl # 2.6.x API change
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_RQ_IS_SYNC], [
 	AC_MSG_CHECKING([whether rq_is_sync() is available])
+	tmp_flags="$EXTRA_KCFLAGS"
+	EXTRA_KCFLAGS="-Wno-unused-but-set-variable"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
 	],[
@@ -15,4 +17,5 @@ AC_DEFUN([ZFS_AC_KERNEL_RQ_IS_SYNC], [
 	],[
 		AC_MSG_RESULT(no)
 	])
+	EXTRA_KCFLAGS="$tmp_flags"
 ])