[libc][cmake] separate installing headers

[michaelrj]

Summary

Now libc headers can be installed separately from installing the rest of
the libc.

[sivachandra]

libc/CMakeLists.txt

153

Since a real target is being added now, the whole block from line 144 to 165 should be moved to right before line 195.

[michaelrj]

libc/CMakeLists.txt

153

I don't think we should move it since LIBC_TARGET and LIBC_COMPONENT are used in some of the folders below. Specifically LIBC_TARGET is used in lib and test and LIBC_COMPONENT is used in lib and loader.

[sivachandra]

libc/CMakeLists.txt

153

Ah, ok! Move just the new install target addition then?

[michaelrj]

move target down

libc/CMakeLists.txt

if(LLVM_LIBC_FULL_BUILD)
   add_subdirectory(utils/HdrGen)
 endif()
 
 set(LIBC_TARGET)
 set(LIBC_COMPONENT)
 set(LIBC_INSTALL_DEPENDS)
 set(LIBC_INSTALL_TARGET)
 if(LLVM_LIBC_FULL_BUILD)
+  add_llvm_install_targets(
+    install-libc-headers
+    DEPENDS libc-headers
+    COMPONENT libc-headers
+  )
   set(LIBC_TARGET libc)
   set(LIBC_COMPONENT libc)
-  set(LIBC_INSTALL_DEPENDS "libc;libc-headers;libc-startup")
+  set(LIBC_INSTALL_DEPENDS "libc;install-libc-headers;libc-startup")
   set(LIBC_INSTALL_TARGET install-libc)
   set(LIBC_ARCHIVE_NAME c)
 else()
   set(LIBC_TARGET llvmlibc)
   set(LIBC_COMPONENT llvmlibc)
   set(LIBC_INSTALL_DEPENDS llvmlibc)
   set(LIBC_INSTALL_TARGET install-llvmlibc)
   set(LIBC_ARCHIVE_NAME llvmlibc)

libc/include/CMakeLists.txt

foreach(target IN LISTS all_install_header_targets)
   if(NOT header_file)
     message(FATAL_ERROR "Installable header file '${target}' does not have the "
                         "HEADER_FILE_PATH property set.")
   endif()
   file(RELATIVE_PATH relative_path ${LIBC_INCLUDE_BINARY_DIR} ${header_file})
   get_filename_component(nested_dir ${relative_path} DIRECTORY)
   install(FILES ${header_file}
           DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/${nested_dir}
-          COMPONENT ${LIBC_COMPONENT})
+          COMPONENT libc-headers)
 endforeach()