getdeps: allow setting per-project install prefix for DESTDIR installs

Summary:
We have a global `--install-prefix` argument that can be used to set
the prefix for all projects, but that is only suitable if you are running with
sufficient privileges to install each of the deps to that location during the
build.  Cmake dependency resolution won't work from the build directory in that
situation; it can only see the final installed location and it will error out
if those files are not present, or link against the currently installed version
instead of the version we just built; not great!

This commit adds a project specific `--project-install-prefix` that can be used
on just the leaf project in a set of deps.  That sidesteps the dependency
concern because only the last stage is built in that mode.  This option
can technically be applied to an arbitrary set of projects, but in light
of the above, in practice it only makes sense to use it for the final
cmake project.  Only the CMakeBuilder respects this option.

In the watchman repo, this commit adjusts the autogen.sh script to allow
specifying the installation prefix; it defaults to `/usr/local` as you
might expect.

refs: https://github.com/facebook/watchman/issues/760

Reviewed By: yfeldblum

Differential Revision: D20674439

fbshipit-source-id: 52799dbd47f3c295e2d6469ee2b74cedeaa20138

build/fbcode_builder/getdeps/builder.py

@@ -19,7 +19,15 @@ from .runcmd import run_cmd
 
 class BuilderBase(object):
     def __init__(
-        self, build_opts, ctx, manifest, src_dir, build_dir, inst_dir, env=None
+        self,
+        build_opts,
+        ctx,
+        manifest,
+        src_dir,
+        build_dir,
+        inst_dir,
+        env=None,
+        final_install_prefix=None,
     ):
         self.env = Env()
         if env:
@@ -35,6 +43,7 @@ class BuilderBase(object):
         self.inst_dir = inst_dir
         self.build_opts = build_opts
         self.manifest = manifest
+        self.final_install_prefix = final_install_prefix
 
     def _get_cmd_prefix(self):
         if self.build_opts.is_windows():
@@ -286,10 +295,24 @@ if __name__ == "__main__":
 """
 
     def __init__(
-        self, build_opts, ctx, manifest, src_dir, build_dir, inst_dir, defines
+        self,
+        build_opts,
+        ctx,
+        manifest,
+        src_dir,
+        build_dir,
+        inst_dir,
+        defines,
+        final_install_prefix=None,
     ):
         super(CMakeBuilder, self).__init__(
-            build_opts, ctx, manifest, src_dir, build_dir, inst_dir
+            build_opts,
+            ctx,
+            manifest,
+            src_dir,
+            build_dir,
+            inst_dir,
+            final_install_prefix=final_install_prefix,
         )
         self.defines = defines or {}
 
@@ -337,7 +360,7 @@ if __name__ == "__main__":
 
     def _compute_cmake_define_args(self, env):
         defines = {
-            "CMAKE_INSTALL_PREFIX": self.inst_dir,
+            "CMAKE_INSTALL_PREFIX": self.final_install_prefix or self.inst_dir,
             "BUILD_SHARED_LIBS": "OFF",
             # Some of the deps (rsocket) default to UBSAN enabled if left
             # unspecified.  Some of the deps fail to compile in release mode
@@ -393,6 +416,8 @@ if __name__ == "__main__":
         reconfigure = reconfigure or self._needs_reconfigure()
 
         env = self._compute_env(install_dirs)
+        if not self.build_opts.is_windows() and self.final_install_prefix:
+            env["DESTDIR"] = self.inst_dir
 
         # Resolve the cmake that we installed
         cmake = path_search(env, "cmake")