Build failure for devel/boost-libs

[Paul Goyette <paul%whooppee.com@localhost>]

I'm getting a build error when building devel/boost-libs.

* Running on an amd64 host, running NetBSD 9.99.15
* My pkgsrc is updated to just a couple hours ago
* Building in a completely empty sandbox (as created by
  sysutils/mksandbox)

The log file shows:

./boost/wave/grammars/cpp_expression_value.hpp:189:43: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]
                     if ((rhs.value.i > 0L && value.i > result) ||
                         ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
./boost/wave/grammars/cpp_expression_value.hpp:256:43: warning: assuming signed overflow does not occur when assuming that (X - c) > X is always false [-Wstrict-overflow]
                     if ((rhs.value.i > 0L && result > value.i) ||
                         ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
gcc.compile.c++ bin.v2/libs/wave/build/gcc-7.4.0/release/link-static/threading-multi/visibility-hidden/instantiate_re2c_lexer_str.o
gcc.compile.c++ bin.v2/libs/wave/build/gcc-7.4.0/release/link-static/threading-multi/visibility-hidden/instantiate_re2c_lexer.o
gcc.archive bin.v2/libs/wave/build/gcc-7.4.0/release/link-static/threadapi-pthread/threading-multi/visibility-hidden/libboost_wave.a
common.copy /tmp/pkgs/devel/boost-libs/work.x86_64/boost_1_71_0/stage/lib/libboost_wave.a
...failed updating 2 targets...
...skipped 13 targets...
...updated 1244 targets...
*** Error code 1

Stop.
make[1]: stopped in /build/pkgsrc/devel/boost-libs
*** Error code 1


+--------------------+--------------------------+-----------------------+
| Paul Goyette       | PGP Key fingerprint:     | E-mail addresses:     |
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