grep: support Perl regular expression

Supporting Perl regular expression is disabled with '--disable-perl-regexp'
but the manpage of 'grep' shows the '-P' option and returns below error:
"/bin/grep.grep -o -P 'PATTERN' file
 /bin/grep.grep: support for the -P option is not compiled into this \
               --disable-perl-regexp binary"

(From OE-Core rev: 8023052653d44a8bbd3618ba700aa260e581036e)

Signed-off-by: Haiqing Bai <Haiqing.Bai@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-extended/grep/grep_3.1.bb

@@ -14,8 +14,6 @@ SRC_URI[sha256sum] = "db625c7ab3bb3ee757b3926a5cfa8d9e1c3991ad24707a83dde8a5ef2b
 
 inherit autotools gettext texinfo pkgconfig
 
-EXTRA_OECONF = "--disable-perl-regexp"
-
 # Fix "Argument list too long" error when len(TMPDIR) = 410
 acpaths = "-I ./m4"
 
@@ -36,6 +34,9 @@ do_install () {
 
 inherit update-alternatives
 
+PACKAGECONFIG ??= "pcre"
+PACKAGECONFIG[pcre] = "--enable-perl-regexp,--disable-perl-regexp,libpcre"
+
 ALTERNATIVE_PRIORITY = "100"
 
 ALTERNATIVE_${PN} = "grep egrep fgrep"