Fix build warnings in xtrabackup.cc

[Valentine Gostev]

While building xtrabackup from source 21 warnings were met:

~# bzr branch lp:percona-xtrabackup
~# cd percona-xtrabackup
~# ./utils/build.sh xtradb > out 2>&1
~# cat out | grep warning
vi.c:1015: warning: ignoring return value of 'write', declared with attribute warn_unused_result
vi.c:1016: warning: ignoring return value of 'write', declared with attribute warn_unused_result
log/log0recv.c:65:1: warning: "RECV_READ_AHEAD_AREA" redefined
./include/log0recv.h:447:1: warning: this is the location of the previous definition
log/log0recv.c:2816: warning: unknown conversion type character ')' in format
mysqld.cc:4404: warning: deprecated conversion from string constant to 'char*'
mysqld.cc:4410: warning: deprecated conversion from string constant to 'char*'
mysqld.cc:4417: warning: deprecated conversion from string constant to 'char*'
mysqld.cc:4432: warning: deprecated conversion from string constant to 'char*'
mysqld.cc:4439: warning: deprecated conversion from string constant to 'char*'
mysqld.cc:4448: warning: deprecated conversion from string constant to 'char*'
xtrabackup.c:2701: warning: format '%02u' expects type 'unsigned int', but argument 3 has type 'char *'
xtrabackup.c:2701: warning: too few arguments for format
xtrabackup.c:5447: warning: format '%lu' expects type 'long unsigned int', but argument 4 has type 'unsigned int'
extract.c:114: warning: incompatible implicit declaration of built-in function 'strlen'
extract.c:448: warning: incompatible implicit declaration of built-in function 'strlen'
util.c:154: warning: field width should have type 'int', but argument 4 has type 'size_t'
util.c:154: warning: field width should have type 'int', but argument 4 has type 'size_t'
util.c:177: warning: field width should have type 'int', but argument 4 has type 'size_t'
util.c:177: warning: field width should have type 'int', but argument 4 has type 'size_t'
libtar.c:271: warning: incompatible implicit declaration of built-in function 'exit'

[Stewart Smith (stewart)]

Marking as Fix Released as we're not seeing any of this in current Jenkins builds.

[Alexey Kopytov (akopytov)]

I actually still see warnings. This one in particular:

log/log0recv.c:65:1: warning: "RECV_READ_AHEAD_AREA" redefined

And tar4ibd ones too. Plus a bunch of other ones that are not mentioned in the original report.

[Alexey Kopytov (akopytov)]

There are still warnings in both 2.0 and 2.1.

[Alexey Kopytov (akopytov)]

The single-binary 2.2 branch build with -Werror in debug mode.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXB-63