Add -lzstd to RT_LIBS and when USE_SYSTEM_LLVM=1 (#59475)

Rather than depending on `llvm-config --system-libs` to link libzstd to
libjulia-internal, we should ask for it explicitly, since we now depend
on it even if LLVM was not configured with zstd.

Possibly fixes the error in
JuliaPackaging/Yggdrasil#11999 (comment)

Author: xal-0

src/Makefile

@@ -160,6 +160,7 @@ ifneq ($(USE_SYSTEM_LLVM),0)
 CG_LLVMLINK += $(LLVM_LDFLAGS) $(shell $(LLVM_CONFIG_HOST) --libs --system-libs)
 LLVM_SHLIB_SYMBOL_VERSION := $(shell readelf -W --dyn-syms $(shell $(LLVM_CONFIG_HOST) --libfiles --link-shared | awk '{print $1; exit}') | \
                                grep _ZN4llvm3Any6TypeId | head -n 1 | sed -ne 's/.*@//p')
+CG_LLVMLINK += -lz -lzstd
 
 # HACK: llvm-config doesn't correctly point to shared libs on all platforms
 #       https://github.com/JuliaLang/julia/issues/29981
@@ -202,7 +203,7 @@ LIBJULIA_PATH_REL := libjulia
 endif
 
 COMMON_LIBPATHS := -L$(build_libdir) -L$(build_shlibdir)
-RT_LIBS := $(WHOLE_ARCHIVE) $(LIBUV) $(WHOLE_ARCHIVE) $(LIBUTF8PROC) $(NO_WHOLE_ARCHIVE) $(LIBUNWIND) $(RT_LLVMLINK) $(OSLIBS) $(LIBTRACYCLIENT) $(LIBITTAPI)
+RT_LIBS := $(WHOLE_ARCHIVE) $(LIBUV) $(WHOLE_ARCHIVE) $(LIBUTF8PROC) $(NO_WHOLE_ARCHIVE) $(LIBUNWIND) $(RT_LLVMLINK) $(OSLIBS) $(LIBTRACYCLIENT) $(LIBITTAPI) -lzstd
 # NB: CG needs uv_mutex_* symbols, but we expect to export them from libjulia-internal
 CG_LIBS := $(LIBUNWIND) $(CG_LLVMLINK) $(OSLIBS) $(LIBTRACYCLIENT) $(LIBITTAPI)