[libc] Fix startup utilities failing to install in full build mode (#82522)

Summary:
Currently, doing `ninja install` will fail in fullbuild mode due to the
startup utilities not being built by default. This was hidden previously
by the fact that if tests were run, it would build the startup utilities
and thus they would be present.

This patch solves this issue by making the `libc-startup` target a
dependncy on the final library. Furthermore we simply factor out the
library install directory into the base CMake directory next to the
include directory handling. This change makes the `crt` files get
installed in `lib/x86_64-unknown-linu-gnu` instead of just `lib`.

This fixes an error I had where doing a runtimes failed to install its
libraries because the install step always errored.

Author: jhuber6

libc/CMakeLists.txt

@@ -225,6 +225,15 @@ else()
   set(LIBC_INSTALL_INCLUDE_DIR ${CMAKE_INSTALL_INCLUDEDIR})
 endif()
 
+if(LIBC_TARGET_TRIPLE)
+  set(LIBC_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LIBC_TARGET_TRIPLE})
+elseif(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT LIBC_GPU_BUILD)
+  set(LIBC_INSTALL_LIBRARY_DIR
+      lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE})
+else()
+  set(LIBC_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX})
+endif()
+
 if(LIBC_TARGET_ARCHITECTURE_IS_GPU)
   include(prepare_libc_gpu_build)
   set(LIBC_ENABLE_UNITTESTS OFF)

libc/lib/CMakeLists.txt

@@ -35,19 +35,13 @@ foreach(archive IN ZIP_LISTS
   )
   if(LLVM_LIBC_FULL_BUILD)
     target_link_libraries(${archive_1} PUBLIC libc-headers)
+    if(TARGET libc-startup)
+      add_dependencies(${archive_1} libc-startup)
+    endif()
   endif()
   list(APPEND added_archive_targets ${archive_1})
 endforeach()
 
-if(LIBC_TARGET_TRIPLE)
-  set(LIBC_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX}/${LIBC_TARGET_TRIPLE})
-elseif(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT LIBC_GPU_BUILD)
-  set(LIBC_INSTALL_LIBRARY_DIR
-      lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE})
-else()
-  set(LIBC_INSTALL_LIBRARY_DIR lib${LLVM_LIBDIR_SUFFIX})
-endif()
-
 install(
   TARGETS ${added_archive_targets}
   ARCHIVE DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}

libc/startup/linux/CMakeLists.txt

@@ -131,7 +131,8 @@ foreach(target IN LISTS startup_components)
   set(fq_target_name libc.startup.linux.${target})
   add_dependencies(libc-startup ${fq_target_name})
   install(FILES $<TARGET_OBJECTS:${fq_target_name}>
-          DESTINATION ${CMAKE_INSTALL_LIBDIR}
+          DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
           RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>
+          EXCLUDE_FROM_ALL
           COMPONENT libc)
 endforeach()