getdeps: Add support for brew packages and define package dependencies

Summary:
In order to speed up build times on a mac, add homebrew support to
getdeps.

Homebrew packages can be declared in a manifest using the `homebrew` header.

Futher, ahornby has added manifest entries for homebrew packages which are
included in this diff and also included a change to use the correct version of
openssl. Without this openssl change, homebrew cmake configure finds an old
openssl 1.0.2 install.

This diff provides a 2x speed up for building folly:

Timings for clean getdeps folly build on mid-2018 2.9Ghz i9 6 core intel macbook pro with 32GB RAM:

With new homebrew system deps:
```
rm -rf /Users/ahornby/.scratch/UsersZahornbyZfbsource/fbcode_builder_getdeps/
time ./opensource/fbcode_builder/getdeps.py build --allow-system-packages folly
real	17m39.329s
user	76m10.317s
sys	5m50.163s
```

Without:
```
rm -rf /Users/ahornby/.scratch/UsersZahornbyZfbsource/fbcode_builder_getdeps/
time ./opensource/fbcode_builder/getdeps.py build folly
real	32m10.344s
user	105m53.448s
sys	15m57.858s
```

Reviewed By: ahornby

Differential Revision: D33842632

fbshipit-source-id: ac785d4a8dcfa31b77292bddd9e747022ac36e3b

build/fbcode_builder/getdeps/buildopts.py

@@ -14,7 +14,7 @@ from typing import Optional, Mapping
 
 from .copytree import containing_repo_type
 from .envfuncs import Env, add_path_entry
-from .fetcher import get_fbsource_repo_data
+from .fetcher import get_fbsource_repo_data, homebrew_package_prefix
 from .manifest import ContextGenerator
 from .platform import HostType, is_windows, get_available_ram
 
@@ -206,6 +206,12 @@ class BuildOptions(object):
             sdkroot = subprocess.check_output(["xcrun", "--show-sdk-path"])
             env["SDKROOT"] = sdkroot.decode().strip()
 
+        # MacOS includes a version of bison so homebrew won't automatically add
+        # its own version to PATH. Find where the homebrew bison is and prepend
+        # it to PATH.
+        if self.is_darwin() and self.host_type.get_package_manager() == "homebrew":
+            add_homebrew_package_to_path(env, "bison")
+
         if self.fbsource_dir:
             env["YARN_YARN_OFFLINE_MIRROR"] = os.path.join(
                 self.fbsource_dir, "xplat/third-party/yarn/offline-mirror"
@@ -300,6 +306,14 @@ class BuildOptions(object):
                         if os.path.isfile(cert_file):
                             env["SSL_CERT_FILE"] = cert_file
 
+        # Try extra hard to find openssl, needed with homebrew on macOS
+        if (
+            self.is_darwin()
+            and "OPENSSL_DIR" not in env
+            and "OPENSSL_ROOT_DIR" in os.environ
+        ):
+            env["OPENSSL_ROOT_DIR"] = os.environ["OPENSSL_ROOT_DIR"]
+
         return env
 
 
@@ -491,3 +505,9 @@ def setup_build_options(args, host_type=None):
         install_dir=args.install_prefix,
         **build_args
     )
+
+
+def add_homebrew_package_to_path(env, package):
+    prefix = homebrew_package_prefix(package)
+    if prefix and os.path.exists(os.path.join(prefix, "bin")):
+        add_path_entry(env, "PATH", os.path.join(prefix, "bin"), append=False)