Boost failed with error C2440 when build with permissive- on MSVC

Hi All,

We tried to build and run hof test for Boost with permissive- mode on VS2017 Update 7 on Windows. It failed to build due to the error C2440. Could you please help take a look at this? Thank you!

**Reproduce steps:**

1. git clone -c core.autocrlf=true --recursive https://github.com/boostorg/boost.git D:\Boost\src
2. open a VS 2015 x86 command prompt and browse to D:\Boost\src
3. set CL=/DNOMINMAX /wd4643 /permissive-
4. .\bootstrap
5. .\b2 headers variant=release --build-dir=..\out\x86rel address-model=32
6. .\b2 variant=release --build-dir=..\out\x86rel address-model=32
7. .\b2 -j4 variant=release --build-dir=..\out\x86rel libs\hof\test

**Failures:**
first_of.cpp
libs\hof\test\first_of.cpp(159): error C2440: 'initializing': cannot convert from 'boost::hof::reveal_adaptor>,boost::hof::detail::static_function_wrapper>>,boost::hof::first_of_adaptor>,boost::hof::detail::static_function_wrapper>>>' to 'boost::hof::reveal_adaptor>,boost::hof::detail::static_function_wrapper>>,boost::hof::first_of_adaptor>,boost::hof::detail::static_function_wrapper>>> &'
with
[
T=conditional_test::
]
libs\hof\test\first_of.cpp(159): note: A non-const reference may only be bound to an lvalue