Argument list too long error from Linux cross-build

["Gary Duzan" <gary%duzan.org@localhost>]

   On a recent Arch Linux x86_64 DOMU with netbsd-7 branch src/xsrc I get:

[root@lnx src]# ./build.sh -r -x -U -m amd64 tools release live-image |& tee ../build-7.log
===> build.sh command:    ./build.sh -r -x -U -m amd64 tools release live-image
===> build.sh started:    Sat Mar 28 23:05:51 EDT 2015
===> NetBSD version:      7.0_BETA
===> MACHINE:             amd64
===> MACHINE_ARCH:        x86_64
===> Build platform:      Linux 3.19.2-1-ARCH x86_64
===> HOST_SH:             /usr/bin/sh
===> Bootstrapping nbmake
[...]
dependall ===> gmp
nbmake[2]: exec(/usr/bin/sh) failed (Argument list too long)

*** Failed target:  dependall
*** Failed command: cd "/opt/netbsd/src/tools/gmp"; /opt/netbsd/src/obj/tooldir.Linux-3.19.2-1-ARCH-x86_64/bin/nbmake realall
*** Error code 1

Stop.
[...]
ERROR: Failed to make build_install in "tools"
*** BUILD ABORTED ***

   Adding -N 4 to the build didn't turn up any more information.
Any ideas where to look for the next clue?

   Thanks.

				Gary Duzan