configure: check for C11 atomics support

Since 3932f8be718fc4ca3b863c51c0d567821d75c003 ("arch/arch.h: Introduce
atomic_{load_acquire,store_release}()") fio has needed C11 atomic
support and this is only provided from gcc 4.9 / clang 3.6 onwards
(http://stdatomic.gforge.inria.fr/#sec-2 ). Make this clearer by
doing the following:

- Add configure check for C11 atomics support and bail out with a
  (friendly) message pointing at compiler version if it's not there
- Remove the minimum compiler version check from compiler.h as it is now
  redundant

I've avoided doing an explicit compiler version check because Apple's
clang can have a wildly different version to upstream
(https://stackoverflow.com/a/33614612 ).

Tested on:
- CentOS 7 with default gcc 4.8.5 (correctly errors with message)
- CentOS 7 docker container using llvm-toolset-7 to provide clang 5.0.1
  (works)
- CentOS 7 docker container using devtool-toolset-7 to provide gcc 7.3.1
  (works)
- Ubuntu 16.04 with clang-3.5 (correctly errors with message)
- Ubuntu 16.04 with clang-3.6 installed (works)
- macOS 10.14.6 with clang-1001.0.46.4 (works)

v2:
- Rebase
- Reword failure message and stop mentioning fio version number

Fixes: https://github.com/axboe/fio/issues/1047
Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>

1 files changed, 19 insertions, 14 deletions

diff --git a/configure b/configure
index 6a7bdeef..25216c63 100755
--- a/configure
+++ b/configure
@@ -496,20 +496,6 @@ else
 fi
 
 ##########################################
-# check compiler version
-
-cat > $TMPC <<EOF
-#include "$(pwd)/compiler/compiler.h"
-int main(void)
-{
-  return 0;
-}
-EOF
-if ! compile_prog "" "" "compiler check"; then
-  fatal "Your compiler is too old, needs GCC 4.9 or higher"
-fi
-
-##########################################
 # check endianness
 if test "$bigendian" != "yes" ; then
   bigendian="no"
@@ -565,6 +551,25 @@ fi
 print_config "Static build" "$build_static"
 
 ##########################################
+# check for C11 atomics support
+cat > $TMPC <<EOF
+#include <stdatomic.h>
+int main(void)
+{
+  _Atomic unsigned v;
+  atomic_load(&v);
+  return 0;
+}
+EOF
+if ! compile_prog "" "" "C11 atomics"; then
+  echo
+  echo "Your compiler doesn't support C11 atomics. gcc 4.9/clang 3.6 are the"
+  echo "minimum versions with it - perhaps your compiler is too old?"
+  fatal "C11 atomics support not found"
+fi
+
+
+##########################################
 # check for wordsize
 wordsize="0"
 cat > $TMPC <<EOF