eglibc: add comment explaining why we pass -O2

While reviewing the eglibc package, Peter mentionned that it would be
good to add a comment that explains why we explicitly build eglibc
with -O2 instead of using the user selected optimization level. This
commit add such a comment.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/eglibc/eglibc.mk

@@ -36,6 +36,9 @@ endif
 #
 #  2. We have to execute the configure script with bash and not sh.
 #
+# Note that as mentionned in
+# http://patches.openembedded.org/patch/38849/, eglibc must be built
+# with -O2, so we pass our own CFLAGS and CXXFLAGS below.
 define EGLIBC_CONFIGURE_CMDS
 	mkdir -p $(@D)/build
 	# Do the configuration