Also suppress Absl warnigs.

cmake/Abseil.cmake

@@ -46,6 +46,14 @@ macro(p4c_obtain_abseil)
     )
     fetchcontent_makeavailable_but_exclude_install(abseil)
 
+    # Suppress warnings for all Abseil targets.
+    get_all_targets(ABSL_BUILD_TARGETS ${absl_BINARY_DIR})
+    foreach(target in ${ABSL_BUILD_TARGETS})
+      if(target MATCHES "absl_*")
+        set_target_properties(${target} PROPERTIES COMPILE_FLAGS "-Wno-error -w")
+      endif()
+    endforeach()
+
     # Reset temporary variable modifications.
     set(CMAKE_UNITY_BUILD ${CMAKE_UNITY_BUILD_PREV})
     set(FETCHCONTENT_QUIET ${FETCHCONTENT_QUIET_PREV})

cmake/P4CUtils.cmake

@@ -433,3 +433,18 @@ macro(fetchcontent_makeavailable_but_exclude_install content)
     add_subdirectory(${${content}_SOURCE_DIR} ${${content}_BINARY_DIR} EXCLUDE_FROM_ALL)
   endif()
 endmacro(fetchcontent_makeavailable_but_exclude_install)
+
+# Collect all currently added targets in all subdirectories
+#
+# Parameters: - _result the list containing all found targets - _dir root directory to start
+# looking from
+# Sourced from https://stackoverflow.com/a/60232044
+function(get_all_targets _result _dir)
+  get_property(_subdirs DIRECTORY "${_dir}" PROPERTY SUBDIRECTORIES)
+  foreach(_subdir IN LISTS _subdirs)
+    get_all_targets(${_result} "${_subdir}")
+  endforeach()
+
+  get_directory_property(_sub_targets DIRECTORY "${_dir}" BUILDSYSTEM_TARGETS)
+  set(${_result} ${${_result}} ${_sub_targets} PARENT_SCOPE)
+endfunction()