We no longer need implicit conversion of options to strings.

We need to install the helper module not just on `etc` but also on all
subdirectories of it too. Also, handle the case where we install
a subdirectory with etc.install.

Closes Homebrew/homebrew#26145.

If you do `brew install blah` it currently doesn't search for it. This
seems to be unintentional looking at this code as the exception thrown
by ARGV.formulae.each is not caught and handled. Instead, let's handle
this case and provide a little more usability around our taps.

Closes Homebrew/homebrew#31761.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Closes Homebrew/homebrew#26481.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

This reverts commit c8d3b39165bb11799d7849ee13a3559ad0bd63f4.

Fixes Homebrew/homebrew#28754.
Fixes Homebrew/homebrew#29846.
Fixes Homebrew/homebrew#30920.

This exception is never used outside of the CxxStdlib class, so we don't
need the Homebrew::InstallationError superclass.

Closes Homebrew/homebrew#31726.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Follow-up to 23d90a6a187a57fbdf4eeac146993e3b37c3d4d9.

Closes Homebrew/homebrew#31706.

Closes Homebrew/homebrew#31628.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

The cxxstdlib_check method currently only supports one value, so we can
just define the accompanying instance method when necessary. If we ever
add more options we can back it with a data structure.

BuildOptions is now immutable (finally).

This flag was supported in gcc-4.0, but not later GCCs or clang.
It pops up in older python-configs, and may also come up in other
contexts.

Fixes mistydemeo/tigerbrew#213.

Closes Homebrew/homebrew#31586.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>