configure: Add a flag to disable seccomp.

This is needed for new arches where libseccomp support doesn't exist
yet.

Fixes #1878.

Makefile.config.in

@@ -7,6 +7,7 @@ ENABLE_S3 = @ENABLE_S3@
 HAVE_SODIUM = @HAVE_SODIUM@
 HAVE_READLINE = @HAVE_READLINE@
 HAVE_BROTLI = @HAVE_BROTLI@
+HAVE_SECCOMP = @HAVE_SECCOMP@
 LIBCURL_LIBS = @LIBCURL_LIBS@
 OPENSSL_LIBS = @OPENSSL_LIBS@
 PACKAGE_NAME = @PACKAGE_NAME@

configure.ac

@@ -186,9 +186,21 @@ AC_SUBST(HAVE_BROTLI, [$have_brotli])
 
 # Look for libseccomp, required for Linux sandboxing.
 if test "$sys_name" = linux; then
+  AC_ARG_ENABLE([seccomp-sandboxing],
+                AC_HELP_STRING([--disable-seccomp-sandboxing],
+                               [Don't build support for seccomp sandboxing (only recommended if your arch doesn't support libseccomp yet!)]
+                              ))
+  if test "x$enable_seccomp_sandboxing" != "xno"; then
     PKG_CHECK_MODULES([LIBSECCOMP], [libseccomp],
                       [CXXFLAGS="$LIBSECCOMP_CFLAGS $CXXFLAGS"])
+    have_seccomp=1
+  else
+    have_seccomp=
   fi
+else
+  have_seccomp=
+fi
+AC_SUBST(HAVE_SECCOMP, [$have_seccomp])
 
 
 # Look for aws-cpp-sdk-s3.

src/libstore/build.cc

@@ -49,7 +49,9 @@
 #include <sys/param.h>
 #include <sys/mount.h>
 #include <sys/syscall.h>
+#if HAVE_SECCOMP
 #include <seccomp.h>
+#endif
 #define pivot_root(new_root, put_old) (syscall(SYS_pivot_root, new_root, put_old))
 #endif
 
@@ -2469,7 +2471,7 @@ void DerivationGoal::chownToBuilder(const Path & path)
 
 void setupSeccomp()
 {
-#if __linux__
+#if __linux__ && HAVE_SECCOMP
     if (!settings.filterSyscalls) return;
 
     scmp_filter_ctx ctx;

src/libstore/local.mk

@@ -25,7 +25,7 @@ ifeq ($(OS), SunOS)
 	libstore_LDFLAGS += -lsocket
 endif
 
-ifeq ($(OS), Linux)
+ifeq ($(HAVE_SECCOMP), 1)
 	libstore_LDFLAGS += -lseccomp
 endif