[libc] Use LIBC_INCLUDE_DIR in tests

[phosek]

Summary

D152592 introduced LIBC_INCLUDE_DIR for the location of the include
directory, use it in tests.

[sivachandra]

Thanks for the cleanup.

libc/cmake/modules/LLVMLibCTestRules.cmake

add_executable(
     EXCLUDE_FROM_ALL
     ${LIBC_UNITTEST_SRCS}
     ${LIBC_UNITTEST_HDRS}
   )
   target_include_directories(
     ${fq_build_target_name}
     PRIVATE
       ${LIBC_SOURCE_DIR}
-      ${LIBC_BUILD_DIR}
-      ${LIBC_BUILD_DIR}/include
+      ${LIBC_INCLUDE_DIR}
   )
   target_compile_options(
     ${fq_build_target_name}
     PRIVATE -fpie ${LIBC_COMPILE_OPTIONS_DEFAULT}
   )
   if(LIBC_UNITTEST_COMPILE_OPTIONS)
     target_compile_options(
       ${fq_build_target_name}
add_executable(
     EXCLUDE_FROM_ALL
     ${LIBC_FUZZER_SRCS}
     ${LIBC_FUZZER_HDRS}
   )
   target_include_directories(
     ${fq_target_name}
     PRIVATE
       ${LIBC_SOURCE_DIR}
-      ${LIBC_BUILD_DIR}
-      ${LIBC_BUILD_DIR}/include
+      ${LIBC_INCLUDE_DIR}
   )
 
   target_link_libraries(${fq_target_name} PRIVATE 
     ${link_object_files} 
     ${LIBC_FUZZER_LINK_LIBRARIES}
   )
 
   set_target_properties(${fq_target_name}
add_executable(
     ${INTEGRATION_TEST_HDRS}
   )
   set_target_properties(${fq_build_target_name}
       PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
   target_include_directories(
     ${fq_build_target_name}
     PRIVATE
       ${LIBC_SOURCE_DIR}
-      ${LIBC_BUILD_DIR}
-      ${LIBC_BUILD_DIR}/include
+      ${LIBC_INCLUDE_DIR}
   )
   target_compile_options(${fq_build_target_name}
       PRIVATE -fpie -ffreestanding -fno-exceptions -fno-rtti ${INTEGRATION_TEST_COMPILE_OPTIONS})
   # The GPU build requires overriding the default CMake triple and architecture.
   if(LIBC_GPU_TARGET_ARCHITECTURE_IS_AMDGPU)
     target_compile_options(${fq_build_target_name} PRIVATE
                            -nogpulib -mcpu=${LIBC_GPU_TARGET_ARCHITECTURE}
                            -flto --target=${LIBC_GPU_TARGET_TRIPLE})
set_target_properties(${fq_build_target_name}
     PROPERTIES
       RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
       #OUTPUT_NAME ${fq_target_name}
   )
   target_include_directories(
     ${fq_build_target_name}
     PRIVATE
       ${LIBC_SOURCE_DIR}
-      ${LIBC_BUILD_DIR}
-      ${LIBC_BUILD_DIR}/include
+      ${LIBC_INCLUDE_DIR}
   )
   target_compile_options(${fq_build_target_name}
       PRIVATE ${LIBC_HERMETIC_TEST_COMPILE_OPTIONS} ${HERMETIC_TEST_COMPILE_OPTIONS})
 
   set(link_libraries "")
   foreach(lib IN LISTS HERMETIC_TEST_LINK_LIBRARIES)
     if(TARGET ${lib}.hermetic)
       list(APPEND link_libraries ${lib}.hermetic)