Warning about unescaped special character when using b2 to run tests.

[WarrenWeckesser]

When I run b2, the first line printed is

Jamfile.v2:1116: Unescaped special character in argument <toolset>msvc:<cxxflags>/fp:precise

Jamfile.v2:1116 is

math/test/Jamfile.v2

Line 1116 in 6dea961

[ run jso_test.cpp : : : <toolset>clang:<cxxflags>-fno-fast-math <toolset>gcc:<cxxflags>-fno-fast-math <toolset>msvc:<cxxflags>/fp:precise [ requires cxx17_if_constexpr cxx17_std_apply ] ]

Chatgp-free says maybe <toolset>msvc:<cxxflags>/fp:precise should be <toolset>msvc:<cxxflags>"/fp:precise" or <toolset>msvc:<cxxflags>/fp\:precise.

I'll let someone more familiar with Jamfiles and Windows figure out the correct incantation and make the change. (I'm running this on Linux.)