fix a/an grammar in obvious cases

adapt to ${CC_WNO_MAYBE_UNINITIALIZED}

Use ${CC_WNO_MAYBE_UNINITIALIZED} instead of
the older style more complex expressions.

Remove workarounds if they were for a specific
version of gcc < 10.

external/bsd/ipf: Fix build failure under LLVM.

-Wno-error= flag now only applies to gcc 8 and not to LLVM based builds.

Reviewed by: kamil@

external/bsd/ipf: Suppress -Werror=maybe-uninitialized error.

Add -Wno-error=maybe-uninitialized in ipsopt.c to prevent build failure.

Error was reported when build.sh was run with MKLIBCSANITIZER=

external/bsd/ipf: Suppress -Werror=maybe-uninitialized error.

Add -Wno-error=maybe-uninitialized in ipsopt.c to prevent build failure.

Error was reported when build.sh was run with MKLIBCSANITIZER=yes flag.

Reviewed by: kamil@

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# There is some very dubious code to locate the values of
# tcb.rcv_adv, tcb.snd_nxt and tcb.rcv_nxt for a socket.
so add: CPPFLAGS+= -D_KMEMUSER

Make this build from our own tree.

Build gluons