[libclc] Stop installing CLC headers (#126908)

The libclc headers are an implementation detail and are not intended to
be used by others as OpenCL headers. The only artifacts of libclc we
want to publish are the LLVM bytecode libraries.

As the headers have been incidentally broken by recent changes, this
commit takes the step to stop installing the headers at all. Downstreams
can use clang's own OpenCL headers, and/or its -fdeclare-opencl-builtins
flag.

Fixes #119967.

(cherry picked from commit a2b0576)

Author: frasercrmck

libclc/CMakeLists.txt

@@ -226,7 +226,6 @@ set( tahiti_aliases pitcairn verde oland hainan bonaire kabini kaveri hawaii
 # pkg-config file
 configure_file( libclc.pc.in libclc.pc @ONLY )
 install( FILES ${CMAKE_CURRENT_BINARY_DIR}/libclc.pc DESTINATION "${CMAKE_INSTALL_DATADIR}/pkgconfig" )
-install( DIRECTORY generic/include/clc DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}" )
 
 if( ENABLE_RUNTIME_SUBNORMAL )
   foreach( file IN ITEMS subnormal_use_default subnormal_disable )

libclc/libclc.pc.in

@@ -1,8 +1,6 @@
-includedir=@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@
 libexecdir=@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_DATADIR@/clc
 
 Name: libclc
 Description: Library requirements of the OpenCL C programming language
 Version: @PROJECT_VERSION@
-Cflags: -I${includedir}
 Libs: -L${libexecdir}