Revert "remove werror"

This reverts commit 983eab7.

Author: vinay-deshmukh

libc/CMakeLists.txt

@@ -34,6 +34,8 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug")
   add_definitions("-D_DEBUG")
 endif()
 
+add_compile_options("-Werror=extra")
+
 # Default to C++17
 set(CMAKE_CXX_STANDARD 17)
 
@@ -58,13 +60,6 @@ set(LIBC_NAMESPACE ${default_namespace}
   CACHE STRING "The namespace to use to enclose internal implementations. Must start with '__llvm_libc'."
 )
 
-# We will build the GPU utilities if we are not doing a runtimes build.
-option(LIBC_BUILD_GPU_LOADER "Always build the GPU loader utilities" OFF)
-if(LIBC_BUILD_GPU_LOADER OR ((NOT LLVM_RUNTIMES_BUILD) AND LLVM_LIBC_GPU_BUILD))
-  add_subdirectory(utils/gpu)
-  return()
-endif()
-
 option(LIBC_CMAKE_VERBOSE_LOGGING
   "Log details warnings and notifications during CMake configuration." OFF)
 
@@ -128,20 +123,25 @@ else()
   endif()
 endif()
 
-option(LLVM_LIBC_FULL_BUILD "Build and test LLVM libc as if it is the full libc" OFF)
+# Defines LIBC_TARGET_ARCHITECTURE and associated macros.
+set(LIBC_TARGET_TRIPLE "" CACHE STRING "The target triple for the libc build.")
+include(LLVMLibCArchitectures)
+
+# Some targets can only support the full build.
+set(default_to_full_build OFF)
+if(LIBC_TARGET_OS_IS_GPU)
+  set(default_to_full_build ON)
+endif()
+
+option(LLVM_LIBC_FULL_BUILD "Build and test LLVM libc as if it is the full libc" ${default_to_full_build})
 option(LLVM_LIBC_IMPLEMENTATION_DEFINED_TEST_BEHAVIOR "Build LLVM libc tests assuming our implementation-defined behavior" ON)
 option(LLVM_LIBC_ENABLE_LINTING "Enables linting of libc source files" OFF)
 
-set(LIBC_TARGET_TRIPLE "" CACHE STRING "The target triple for the libc build.")
-
 option(LIBC_CONFIG_PATH "The path to user provided folder that configures the build for the target system." OFF)
 
 set(LIBC_ENABLE_UNITTESTS ON)
 set(LIBC_ENABLE_HERMETIC_TESTS ${LLVM_LIBC_FULL_BUILD})
 
-# Defines LIBC_TARGET_ARCHITECTURE and associated macros.
-include(LLVMLibCArchitectures)
-
 set(LIBC_CONFIG_JSON_FILE_LIST "")
 
 if(NOT LIBC_CONFIG_PATH)