meson: pass docdir option

When cross-compiling, by default qemu_docdir is 'c:\Program Files\QEMU\'
which is not recognized as being an absolute path, and meson will end up
adding the prefix again.

Add an option to pass docdir location to meson, pre-prefixed like we do
with other directories, build qemu_docdir with the common suffix and use
that instead of config_host['qemu_docdir'].

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20200826110419.528931-7-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/meson_options.txt b/meson_options.txt
index f427569..c3120fa 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -1,5 +1,7 @@
 option('qemu_suffix', type : 'string', value: 'qemu',
        description: 'Suffix for QEMU data/modules/config directories (can be empty)')
+option('docdir', type : 'string', value : 'doc',
+       description: 'Base directory for documentation installation (can be empty)')
 option('gettext', type : 'boolean', value : true)
 option('sdl', type : 'feature', value : 'auto')
 option('sdl_image', type : 'feature', value : 'auto')