Update header_namespace for OSS

Summary: fizz might depend on a folly header like `<folly/portability/Sys.h>`, but due to the layout of the repo buck2 actually places this header at `<folly/folly/portability/Sys.h>`

Reviewed By: ajb85

Differential Revision: D58272254

fbshipit-source-id: 3abc6240a83b6dc8036dc88b704c816bc7946e62

shim/shims.bzl

@@ -137,18 +137,22 @@ def cpp_library(
         private_headers = None,
         propagated_pp_flags = (),
         **kwargs):
+    base_path = native.package_name()
+    oss_depends_on_folly = read_config("oss_depends_on", "folly", False)
+    header_base_path = base_path
+    if oss_depends_on_folly and header_base_path.startswith("folly"):
+        header_base_path = header_base_path.replace("folly/", "", 1)
+
     _unused = (undefined_symbols, arch_preprocessor_flags, modular_headers, arch_compiler_flags, tags, propagated_pp_flags)  # @unused
     if os_deps:
         deps += _select_os_deps(_fix_dict_deps(os_deps))
     if headers == None:
         headers = []
     if tags != None and "oss_dependency" in tags:
-        oss_depends_on_folly = read_config("oss_depends_on", "folly", False)
         if oss_depends_on_folly:
             headers = [item.replace("//:", "//folly:") if item == "//:folly-config.h" else item for item in headers]
     if is_select(srcs) and auto_headers == AutoHeaders.SOURCES:
         # Validate `srcs` and `auto_headers` before the config check
-        base_path = native.package_name()
         fail(
             "//{}:{}: `select` srcs cannot support AutoHeaders.SOURCES".format(base_path, name),
         )
@@ -178,6 +182,7 @@ def cpp_library(
         headers = private_headers,
         exported_linker_flags = linker_flags,
         linker_flags = private_linker_flags,
+        header_namespace = header_base_path,
         **kwargs
     )