Use .p2align in ASMALIGN() macro

The test for .align syntax was apparently unreliable with some compilers.
Using the .p2align directive instead avoids the need for this test.

Originally committed as revision 23428 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2794,9 +2794,6 @@ if enabled gprof; then
     add_ldflags -p
 fi
 
-# Find out if the .align argument is a power of two or not.
-check_asm asmalign_pot '".align 3"'
-
 enabled_any $THREADS_LIST      && enable threads
 
 check_deps $CONFIG_LIST       \
@@ -2819,7 +2816,6 @@ enabled asm || { arch=c; disable $ARCH_LIST $ARCH_EXT_LIST; }
 echo "install prefix            $prefix"
 echo "source path               $source_path"
 echo "C compiler                $cc"
-echo ".align is power-of-two    $asmalign_pot"
 echo "ARCH                      $arch ($cpu)"
 if test "$build_suffix" != ""; then
     echo "build suffix              $build_suffix"
@@ -3051,8 +3047,6 @@ get_version LIBAVFORMAT libavformat/avformat.h
 get_version LIBAVUTIL   libavutil/avutil.h
 get_version LIBAVFILTER libavfilter/avfilter.h
 
-enabled asmalign_pot || align_shift="1 <<"
-
 cat > $TMPH <<EOF
 /* Automatically generated by configure - do not modify! */
 #ifndef FFMPEG_CONFIG_H
@@ -3063,7 +3057,7 @@ cat > $TMPH <<EOF
 #define CC_TYPE "$cc_type"
 #define CC_VERSION $cc_version
 #define restrict $_restrict
-#define ASMALIGN(ZEROBITS) ".align $align_shift " #ZEROBITS "\\n\\t"
+#define ASMALIGN(ZEROBITS) ".p2align " #ZEROBITS "\\n\\t"
 #define EXTERN_PREFIX "${extern_prefix}"
 #define EXTERN_ASM ${extern_prefix}
 EOF