[libclc] Fix building top-level 'libclc' target (#150972)

With libclc being a 'runtime', the top-level build assumes that there is
a corresopnding 'libclc' target. We previously weren't providing this,
leading to a build failure if the user tried to build it.

This commit remedies this by adding support for building the 'libclc'
target. It does so by adding dependencies from the OpenCL builtins to
this target. It uses a configurable in-between target -
libclc-opencl-builtins - to ease the possibility of adding non-OpenCL
builtin libraries in the future.

libclc/CMakeLists.txt

@@ -42,6 +42,12 @@ set( LIBCLC_TARGETS_TO_BUILD "all"
 
 option( ENABLE_RUNTIME_SUBNORMAL "Enable runtime linking of subnormal support." OFF )
 
+# Top level target used to build all Libclc libraries.
+add_custom_target( libclc ALL )
+
+add_custom_target( libclc-opencl-builtins COMMENT "Build libclc OpenCL builtins" )
+add_dependencies( libclc libclc-opencl-builtins )
+
 if( LIBCLC_STANDALONE_BUILD OR CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )
   # Out-of-tree configuration
   set( LIBCLC_STANDALONE_BUILD TRUE )
@@ -463,6 +469,7 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
       LIB_FILES ${opencl_lib_files}
       GEN_FILES ${opencl_gen_files}
       ALIASES ${${d}_aliases}
+      PARENT_TARGET libclc-opencl-builtins
       # Link in the CLC builtins and internalize their symbols
       INTERNAL_LINK_DEPENDENCIES builtins.link.clc-${arch_suffix}
     )

libclc/cmake/modules/AddLibclc.cmake

@@ -207,6 +207,8 @@ endfunction()
 #      libclc architecture/triple suffix
 #  * TRIPLE <string>
 #      Triple used to compile
+#  * PARENT_TARGET <string>
+#      Target into which to group the target builtins
 #
 # Optional Arguments:
 # * CLC_INTERNAL
@@ -229,7 +231,7 @@ endfunction()
 function(add_libclc_builtin_set)
   cmake_parse_arguments(ARG
     "CLC_INTERNAL"
-    "ARCH;TRIPLE;ARCH_SUFFIX"
+    "ARCH;TRIPLE;ARCH_SUFFIX;PARENT_TARGET"
     "LIB_FILES;GEN_FILES;COMPILE_FLAGS;OPT_FLAGS;ALIASES;INTERNAL_LINK_DEPENDENCIES"
     ${ARGN}
   )
@@ -403,6 +405,9 @@ function(add_libclc_builtin_set)
     add_custom_target( prepare-${ARG_TRIPLE} ALL )
   endif()
   add_dependencies( prepare-${ARG_TRIPLE} prepare-${obj_suffix} )
+  # Add dependency to top-level pseudo target to ease making other
+  # targets dependent on libclc.
+  add_dependencies( ${ARG_PARENT_TARGET} prepare-${ARG_TRIPLE} )
 
   install(
     FILES ${libclc_builtins_lib}
@@ -445,6 +450,7 @@ function(add_libclc_builtin_set)
     add_custom_target( alias-${alias_suffix} ALL
       DEPENDS ${LIBCLC_OUTPUT_LIBRARY_DIR}/${alias_suffix}
     )
+    add_dependencies( ${ARG_PARENT_TARGET} alias-${alias_suffix} )
     set_target_properties( alias-${alias_suffix}
       PROPERTIES FOLDER "libclc/Device IR/Aliases"
     )