Update protobuf to 29.6 and remove abseil GCC >14 workarounds (#5550)

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: fruffy <[email protected]>

Author: Copilot

cmake/Abseil.cmake

@@ -54,20 +54,10 @@ macro(p4c_obtain_abseil)
         # Do not suppress warnings for Abseil library targets that are aliased.
         get_target_property(target_type ${target} TYPE)
         if (NOT ${target_type} STREQUAL "INTERFACE_LIBRARY")
-          # We need this workaround because of https://github.com/abseil/abseil-cpp/issues/1664.
-          # TODO: Remove once the Abseil compilation issue is fixed.
-          if (CMAKE_COMPILER_IS_GNUCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 14)
-            target_compile_options(${target} PUBLIC "-mbmi")
-          endif()
           target_compile_options(${target} PRIVATE "-Wno-error" "-w")
         endif()
       endif()
     endforeach()
-    # TODO: Remove once the Abseil compilation issue is fixed.
-    if (CMAKE_COMPILER_IS_GNUCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 14)
-      message(WARNING "Compiling with GCC > 14. Adding -mbmi to Abseil targets, this may cause incompatibility with old CPUs.")
-    endif()
-
     # Reset temporary variable modifications.
     set(CMAKE_UNITY_BUILD ${CMAKE_UNITY_BUILD_PREV})
     set(FETCHCONTENT_QUIET ${FETCHCONTENT_QUIET_PREV})

cmake/Protobuf.cmake

@@ -1,5 +1,5 @@
 macro(p4c_obtain_protobuf)
-  set(P4C_PROTOBUF_VERSION 25.3)
+  set(P4C_PROTOBUF_VERSION 29.6)
   option(
     P4C_USE_PREINSTALLED_PROTOBUF
     "Look for a preinstalled version of Protobuf in the system instead of installing a prebuilt binary using FetchContent."
@@ -63,7 +63,7 @@ macro(p4c_obtain_protobuf)
     fetchcontent_declare(
       protobuf
       URL https://github.com/protocolbuffers/protobuf/releases/download/v${P4C_PROTOBUF_VERSION}/protobuf-${P4C_PROTOBUF_VERSION}.tar.gz
-      URL_HASH SHA256=d19643d265b978383352b3143f04c0641eea75a75235c111cc01a1350173180e
+      URL_HASH SHA256=877bf9f880631aa31daf2c09896276985696728137fcd43cc534a28c5566d9ba
       USES_TERMINAL_DOWNLOAD TRUE
       GIT_PROGRESS TRUE
       DOWNLOAD_EXTRACT_TIMESTAMP TRUE