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/fetcher.py

@@ -158,6 +158,7 @@ class SystemPackageFetcher(object):
     def __init__(self, build_options, packages):
         self.manager = build_options.host_type.get_package_manager()
         self.packages = packages.get(self.manager)
+        self.host_type = build_options.host_type
         if self.packages:
             self.installed = None
         else:
@@ -172,6 +173,8 @@ class SystemPackageFetcher(object):
             cmd = ["rpm", "-q"] + sorted(self.packages)
         elif self.manager == "deb":
             cmd = ["dpkg", "-s"] + sorted(self.packages)
+        elif self.manager == "homebrew":
+            cmd = ["brew", "ls", "--versions"] + sorted(self.packages)
 
         if cmd:
             proc = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
@@ -181,9 +184,23 @@ class SystemPackageFetcher(object):
             else:
                 # Need all packages to be present to consider us installed
                 self.installed = False
+
         else:
             self.installed = False
 
+        # Hack to make openssl discovery with homebrew work. If openssl was
+        # built with autoconf we could use autoconf.envcmd.OPENSSL_ROOT_DIR
+        # from the manifest, but it isn't, so handle the special case here.
+        if (
+            self.installed
+            and self.host_type.is_darwin()
+            and self.manager == "homebrew"
+            and "openssl@1.1" in self.packages
+        ):
+            candidate = homebrew_package_prefix("openssl@1.1")
+            if os.path.exists(candidate):
+                os.environ["OPENSSL_ROOT_DIR"] = candidate
+
         return bool(self.installed)
 
     def update(self):
@@ -789,3 +806,14 @@ class ArchiveFetcher(Fetcher):
 
     def get_src_dir(self):
         return self.src_dir
+
+
+def homebrew_package_prefix(package):
+    cmd = ["brew", "--prefix", package]
+    try:
+        proc = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    except FileNotFoundError:
+        return
+
+    if proc.returncode == 0:
+        return proc.stdout.decode("utf-8").rstrip()