disable lbutils on non-linux systems

i should probably test musl as well, on linux

libreboot-utils is stable on the glibc systems i tested
with linux. it is quite buggy on bsd systems.

it's irresponsible to let users compile this until i've
properly tested the code. putting this error in for now.

i made lbmk use the old nvmutil version for now, and retro
fitted several improvements to i/o there from lbutils,
changes that i know are stable on bsd.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/libreboot-utils/lottery.c

@@ -16,6 +16,9 @@ exit_cleanup(void);
 int
 main(int argc, char **argv)
 {
+#ifndef __linux__
+#error This code is currently buggy on BSD systems. Only use on Linux.
+#endif
 	int same = 0;
 	char *buf;
 	size_t size = BUFSIZ;

util/libreboot-utils/mkhtemp.c

@@ -41,6 +41,9 @@ exit_cleanup(void);
 int
 main(int argc, char *argv[])
 {
+#ifndef __linux__
+#error This code is currently buggy on BSD systems. Only use on Linux.
+#endif
 	size_t len;
 	size_t tlen;
 	size_t xc = 0;

util/libreboot-utils/nvmutil.c

@@ -27,6 +27,9 @@ exit_cleanup(void);
 int
 main(int argc, char *argv[])
 {
+#ifndef __linux__
+#error This code is currently buggy on BSD systems. Only use on Linux.
+#endif
 	struct xstate *x;
 	struct commands *cmd;
 	struct xfile *f;