The attached patch fixes the problem and is what we use in Spack to
make GCC build with zstd support.
gcc/
* Makefile.in (ZSTD_INC): Define.
(ZSTD_LIB): Include ZSTD_LDFLAGS.
(CFLAGS-lto-compress.o): Add ZSTD_INC.
* configure.ac (ZSTD_CPPFLAGS, ZSTD_LDFLAGS): New variables for
AC_SUBST.
* configure: Rebuilt.
# Libs needed (at present) just for jcf-dump.
LDEXP_LIB = @LDEXP_LIB@
-ZSTD_LIB = @ZSTD_LIB@
+ZSTD_INC = @ZSTD_CPPFLAGS@
+ZSTD_LIB = @ZSTD_LDFLAGS@ @ZSTD_LIB@
# Likewise, for use in the tools that must run on this machine
# even if we are cross-building GCC.
version.o: $(REVISION) $(DATESTAMP) $(BASEVER) $(DEVPHASE)
# lto-compress.o needs $(ZLIBINC) added to the include flags.
-CFLAGS-lto-compress.o += $(ZLIBINC)
+CFLAGS-lto-compress.o += $(ZLIBINC) $(ZSTD_INC)
CFLAGS-lto-streamer-in.o += -DTARGET_MACHINE=\"$(target_noncanonical)\"
LIBICONV
ZSTD_LIB
ZSTD_INCLUDE
+ZSTD_LDFLAGS
+ZSTD_CPPFLAGS
DL_LIB
LDEXP_LIB
EXTRA_GCC_LIBS
AC_SUBST(ZSTD_LIB)
ZSTD_CPPFLAGS=
ZSTD_LDFLAGS=
+AC_SUBST(ZSTD_CPPFLAGS)
+AC_SUBST(ZSTD_LDFLAGS)
AC_ARG_WITH(zstd,
[AS_HELP_STRING([--with-zstd=PATH],
[specify prefix directory for installed zstd library.