libc6: improve reproducibility

Building various libraries (libc6, libc6-pic, libc6-staticdev, libc6-dbg, ...)
can be non-deterministic because they may be built with two different versions
of intl/plural.c. in two otherwise identical builds. We may or may not re-generate
the file plural.c from the file plural.y, based on bison being installed or not
and based on mtimes of those two files, as the Makefile contains:

plural.c: plural.y
	$(BISON) $(BISONFLAGS) $@ $^

If the above rule does not fire, we use a "fallback" plural.c, otherwise
we use plural.c re-generated from plural.y.
The fix is to always require bison to be installed and unconditionally
re-generate plural.c. (This is achieved by touching plural.y).

[YOCTO #12291]

(From OE-Core rev: b79eeb68c6ad7c92a3e54c6f97a8bf49f0098206)

Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/glibc/glibc_2.26.bb

@@ -5,7 +5,7 @@ LIC_FILES_CHKSUM = "file://LICENSES;md5=e9a558e243b36d3209f380deb394b213 \
       file://posix/rxspencer/COPYRIGHT;md5=dc5485bb394a13b2332ec1c785f5d83a \
       file://COPYING.LIB;md5=4fbd65380cdd255951079008b364516c"
 
-DEPENDS += "gperf-native"
+DEPENDS += "gperf-native bison-native"
 
 SRCREV ?= "77f921dac17c5fa99bd9e926d926c327982895f7"
 
@@ -106,6 +106,10 @@ do_configure () {
 # version check and doesn't really help with anything
         (cd ${S} && gnu-configize) || die "failure in running gnu-configize"
         find ${S} -name "configure" | xargs touch
+        # "plural.c" may or may not get regenerated from "plural.y" so we
+        # touch "plural.y" to make sure it does. (This should not be needed
+        # for glibc version 2.26+)
+        find ${S}/intl -name "plural.y" | xargs touch
         CPPFLAGS="" oe_runconf
 }