upb: the triumphant return of upb/mem:internal

PiperOrigin-RevId: 593835739

upb/BUILD

@@ -395,6 +395,7 @@ upb_amalgamation(
         ":reflection_internal",
         ":wire",
         ":wire_reader",
+        "//upb/mem:internal",
     ],
     strip_import_prefix = ["src"],
 )
@@ -441,6 +442,7 @@ upb_amalgamation(
         ":reflection_internal",
         ":wire",
         ":wire_reader",
+        "//upb/mem:internal",
     ],
     prefix = "php-",
     strip_import_prefix = ["src"],
@@ -488,6 +490,7 @@ upb_amalgamation(
         ":reflection_internal",
         ":wire",
         ":wire_reader",
+        "//upb/mem:internal",
     ],
     prefix = "ruby-",
     strip_import_prefix = ["src"],

upb/mem/BUILD

@@ -17,6 +17,18 @@ cc_library(
         "alloc.h",
         "arena.h",
         "arena.hpp",
+    ],
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+    deps = [
+        ":internal",
+        "//upb:port",
+    ],
+)
+
+cc_library(
+    name = "internal",
+    hdrs = [
         "internal/arena.h",
     ],
     copts = UPB_DEFAULT_COPTS,

upb/wire/BUILD

@@ -37,6 +37,7 @@ cc_library(
         "//upb:message_types",
         "//upb:mini_table",
         "//upb:port",
+        "//upb/mem:internal",
         "//third_party/utf8_range",
     ],
 )