llvm: Move libprivatelldb to the lldb package

Set PACKAGE=lldb in lldb.pre.mk rather than in individual Makefiles;
change lib/clang/Makefile.inc from PACKAGE=clang to PACKAGE?=clang to
avoid overwriting it.

This is safe to MFC to stable/15 since the moved library will be
picked up automatically by pkg.

MFC after:	2 weeks
Reviewed by:	emaste
Sponsored by:	https://www.patreon.com/bsdivy
Differential Revision:	https://reviews.freebsd.org/D56674

lib/clang/Makefile.inc

@@ -1,6 +1,6 @@
 .include <src.opts.mk>
 
-PACKAGE=	clang
+PACKAGE?=	clang
 MK_PIE:=	no	# Explicit libXXX.a references
 
 .if ${MK_LLVM_FULL_DEBUGINFO} == "no"

lib/clang/liblldb/Makefile

@@ -6,7 +6,6 @@
 LIB=		lldb
 INTERNALLIB=
 .else
-PACKAGE=	lldb
 SHLIB_CXX=	lldb
 SHLIB_MAJOR=	21
 PRIVATELIB=

lib/clang/lldb.pre.mk

@@ -1,4 +1,6 @@
 
 .include "clang.pre.mk"
 
+PACKAGE=	lldb
+
 LLDB_SRCS=	${LLVM_BASE}/lldb

usr.bin/clang/lldb-server/Makefile

@@ -1,6 +1,5 @@
 .include "${SRCTOP}/lib/clang/lldb.pre.mk"
 
-PACKAGE=	lldb
 PROG_CXX=	lldb-server
 
 CFLAGS+=	-I${LLDB_SRCS}/include

usr.bin/clang/lldb/Makefile

@@ -1,6 +1,5 @@
 .include "${SRCTOP}/lib/clang/lldb.pre.mk"
 
-PACKAGE=	lldb
 PROG_CXX=	lldb
 
 CFLAGS+=	-I${LLDB_SRCS}/include