configure: use .altmacro for gnu as check on arm

Clang's integrated assembler (after 3.4) does not yet support the
'.altmacro' directive which is only used in arm asm. Support is planned:
http://llvm.org/bugs/show_bug.cgi?id=18918

1 files changed, 4 insertions, 0 deletions

diff --git a/configure b/configure
index 59f7273581..8359c68b13 100755
--- a/configure
+++ b/configure
@@ -3736,6 +3736,10 @@ if enabled asm; then
 m x
 EOF
 
+    check_as <<EOF || $nogas "GNU assembler not found, install gas-preprocessor"
+.altmacro
+EOF
+
     check_as <<EOF && enable as_func
 .func test
 .endfunc