The `install_headers` function now has an optional argument
`preserve_path` that allows installing multi-directory
headerfile structures that live alongside sourcecode with a
single command.
For example, the headerfile structure
headers = [
'one.h',
'two.h',
'alpha/one.h',
'alpha/two.h',
'alpha/three.h'
'beta/one.h'
]
can now be passed to `install_headers(headers, subdir: 'mylib', preserve_path: true)`
and the resulting directory tree will look like
{prefix}
└── include
└── mylib
├── alpha
│ ├── one.h
│ ├── two.h
│ └── three.h
├── beta
│ └── one.h
├── one.h
└── two.h
Fixes#3371
ad8f24f232