Finally, fix Zstd kernel build on MIPS and RISC-V

Add an implementation of the intrinsics invoked by __builtin_ctz{,ll} and
__builtin_clz{,ll}, and include this compilation unit on platforms that lack
assembly intrinsics for those builtins (MIPS and RISC-V).

Future cleanup work might involve bringing these into a mini libcompiler-rt
for the standalone kernel environment.  Or cleaning up the approach upstream
takes for builtins in standalone environments (or just FreeBSD).  For now,
at least this builds, and doesn't require modifying the vendor code.

Reported by:	jeff, markj, mizhka
Reviewed by:	jhb (earlier version), rpokala (comment text earlier version)
Sponsored by:	Dell EMC Isilon

sys/conf/files.mips

@@ -112,3 +112,6 @@ cddl/compat/opensolaris/kern/opensolaris_atomic.c	optional zfs | dtrace compile-
 cddl/dev/dtrace/mips/dtrace_asm.S			optional dtrace compile-with "${DTRACE_S}"
 cddl/dev/dtrace/mips/dtrace_subr.c			optional dtrace compile-with "${DTRACE_C}"
 cddl/dev/fbt/mips/fbt_isa.c				optional dtrace_fbt | dtraceall compile-with "${FBT_C}"
+
+# Zstd
+contrib/zstd/lib/freebsd/zstd_kfreebsd.c		standard compile-with ${ZSTD_C}

sys/conf/files.riscv

@@ -56,3 +56,6 @@ riscv/riscv/uio_machdep.c	standard
 riscv/riscv/uma_machdep.c	standard
 riscv/riscv/unwind.c		optional	ddb | kdtrace_hooks | stack
 riscv/riscv/vm_machdep.c	standard
+
+# Zstd
+contrib/zstd/lib/freebsd/zstd_kfreebsd.c		standard compile-with ${ZSTD_C}

sys/contrib/zstd/lib/freebsd/zstd_kfreebsd.c

@@ -0,0 +1,75 @@
+/*-
+ * Copyright (c) 2018 Conrad Meyer <cem@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#include "zstd_kfreebsd.h"
+
+/*
+ * The kernel as a standalone target does not link against libgcc or
+ * libcompiler-rt. On platforms (e.g., MIPS and RISCV) that do not have a
+ * direct assembly implementation of the relevant builtin functions that zstd
+ * references, the compiler converts them into calls to the runtime library
+ * intrinsics.  Since the kernel does not link against the runtime libraries,
+ * this results in a failure to link the kernel.
+ *
+ * The goal of the following definitions is to use supported kernel constructs
+ * to implement the same functionality, without adding diff to the Zstd contrib
+ * code.
+ *
+ * A subsequent enhancement might create a mini compiler-rt library for kernel
+ * use and move these over there instead.
+ */
+
+/* Count trailing zeros */
+int
+__ctzsi2(int x)
+{
+       if (x == 0)
+               return (sizeof(x) * NBBY);
+       return (ffs(x) - 1);
+}
+
+long long
+__ctzdi2(long long x)
+{
+       if (x == 0)
+               return (sizeof(x) * NBBY);
+       return (ffsll(x) - 1);
+}
+
+/* Count leading zeros */
+int
+__clzsi2(int x)
+{
+       return (sizeof(x) * NBBY - fls(x));
+}
+
+long long
+__clzdi2(long long x)
+{
+       return (sizeof(x) * NBBY - flsll(x));
+}