configure.ac: remove another uname check

uname checks are not cross-safe.

The normalization for Cygwin doesn't need any equivalent for host_os
because nothing actually checked whether sys_name was cygwin any more.

(cherry picked from commit cff8fd69b6)

configure.ac

@@ -33,14 +33,6 @@ AC_ARG_WITH(system, AC_HELP_STRING([--with-system=SYSTEM],
         system="$machine_name-`echo $host_os | "$SED" -e's/@<:@0-9.@:>@*$//g'`";;
    esac])
 
-sys_name=$(uname -s | tr 'A-Z ' 'a-z_')
-
-case $sys_name in
-    cygwin*)
-        sys_name=cygwin
-        ;;
-esac
-
 AC_MSG_RESULT($system)
 AC_SUBST(system)
 AC_DEFINE_UNQUOTED(SYSTEM, ["$system"], [platform identifier ('cpu-os')])
@@ -67,10 +59,12 @@ AC_SYS_LARGEFILE
 
 # Solaris-specific stuff.
 AC_STRUCT_DIRENT_D_TYPE
-if test "$sys_name" = sunos; then
+case "$host_os" in
+  solaris*)
     # Solaris requires -lsocket -lnsl for network functions
     LDFLAGS="-lsocket -lnsl $LDFLAGS"
-fi
+    ;;
+esac
 
 
 # Check for pubsetbuf.
@@ -231,7 +225,8 @@ PKG_CHECK_MODULES([LIBBROTLI], [libbrotlienc libbrotlidec], [CXXFLAGS="$LIBBROTL
 
 
 # Look for libseccomp, required for Linux sandboxing.
-if test "$sys_name" = linux; then
+case "$host_os" in
+  linux*)
     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!)]
@@ -244,9 +239,11 @@ if test "$sys_name" = linux; then
     else
       have_seccomp=
     fi
-else
+    ;;
+  *)
     have_seccomp=
-fi
+    ;;
+esac
 AC_SUBST(HAVE_SECCOMP, [$have_seccomp])