Fix libiberty install and shared glog for folly-python

Summary:
Fixes the two getdeps regressions that break the BGP++ OSS builds (`fboss-oss-build-bgp`, `fboss-oss-build-bgp-bb`) and FBOSS OSS builds that build dependencies from HEAD. They ship together because either fix alone still leaves `fboss-oss-build-ondiff` red on the other.

libiberty: getdeps-built libiberty installs its headers but no `libiberty.a`, so `fbthrift-python` configure fails with `Could NOT find Libiberty (missing: LIBIBERTY_LIBRARY)`. `AutoconfBuilder` adds `--disable-shared` when a manifest passes neither shared flag, and libiberty's configure then empties `PICFLAG`, so `pic/libiberty.a` is never built and `libiberty_install_pic_lib.patch` copies nothing while the install still exits 0. The miss was silent until D125047475 renamed the package in `FindLibiberty.cmake` to `Libiberty`, which made `find_package(Libiberty REQUIRED)` in fbthrift enforce REQUIRED. Passing `--enable-shared` keeps `PICFLAG`; libiberty builds no shared library either way.

glog: since D124075105 made glog static by default, the `-python` shared libraries built on `folly-python` each embed a copy of glog, and every copy registers its flags with the one shared gflags, so test binaries abort with `linked both statically and dynamically`. glog's `[cmake.defines.feature_shared_libs=on]` could never turn on because glog declared no features. This declares `shared_libs` in glog and requests it from `folly-python`; getdeps unions features per project, so graphs that contain `folly-python` (`bgp`, `fboss`) get one shared glog, and graphs without it (`cachelib`, `mcrouter`, `folly`, `fbthrift`) keep static glog.

Reviewed By: yfeldblum, shitanshu-shah

Differential Revision: D125332467

fbshipit-source-id: 4ff0cb077de91afc86f79f09e1ab6b15fac2c7f0

build/fbcode_builder/manifests/folly-python

@@ -16,7 +16,9 @@ builder = nop
 
 [dependencies]
 gflags
-glog
+# folly-python's shared libraries and the binaries that load them must use one
+# copy of glog.
+glog = shared_libs
 googletest
 boost-python
 libdwarf-python

build/fbcode_builder/manifests/glog

@@ -23,6 +23,9 @@ patchfile = glog_default_visibility.patch
 [dependencies]
 gflags
 
+[features]
+shared_libs =
+
 [cmake.defines]
 BUILD_TESTING=NO
 WITH_PKGCONFIG=ON

build/fbcode_builder/manifests/libiberty

@@ -24,3 +24,6 @@ patchfile = libiberty_install_pic_lib.patch
 # as we still want to use system linker and assembler etc
 [autoconf.args]
 --enable-install-libiberty
+# libiberty builds pic/libiberty.a, the archive that
+# libiberty_install_pic_lib.patch installs, only when shared is enabled.
+--enable-shared

build/fbcode_builder/manifests/libiberty-python

@@ -30,5 +30,8 @@ builder = nop
 # as we still want to use system linker and assembler etc
 [autoconf.args]
 --enable-install-libiberty
+# libiberty builds pic/libiberty.a, the archive that
+# libiberty_install_pic_lib.patch installs, only when shared is enabled.
+--enable-shared
 CFLAGS=-fPIC -O2
 PICFLAG=-fPIC