Use atomics in guard.cc / remove special casing in targets.

The PowerPC, AIX, Alpha, IA64  implementations of atomic_word.h are in no
way different from what can be achieved with the generic rewrite in
Patch 1 of this series - delete these.

2015-06-12  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

        * config/cpu/alpha/atomic_word.h: Remove.
        * config/cpu/ia64/atomic_word.h: Remove.
        * config/cpu/powerpc/atomic_word.h: Remove.
        * config/os/aix/atomic_word.h: Remove.
        * configure.host (atomic_word_dir) [ia64, aix*, powerpc, alpha]:
        Use generic definition.

From-SVN: r224412

libstdc++-v3/ChangeLog

 2015-06-12  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
 
+	PR c++/66192
+	PR target/66200
+        * config/cpu/alpha/atomic_word.h: Remove.
+        * config/cpu/ia64/atomic_word.h: Remove.
+        * config/cpu/powerpc/atomic_word.h: Remove.
+        * config/os/aix/atomic_word.h: Remove.
+        * configure.host (atomic_word_dir) [ia64, aix*, powerpc, alpha]:
+        Use generic definition.
+
+2015-06-12  Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>
+
 	PR target/66200
 	PR c++/66192
 	* * config/cpu/generic/atomic_word.h (_GLIBCXX_READ_MEM_BARRIER): Define

libstdc++-v3/configure.host

@@ -156,21 +156,12 @@ esac
 # Most can just use generic.
 # THIS TABLE IS SORTED.  KEEP IT THAT WAY.
 case "${host_cpu}" in
-  alpha*)
-    atomic_word_dir=cpu/alpha
-    ;;
   cris*)
     atomic_word_dir=cpu/cris
     ;;
-  ia64)
-    atomic_word_dir=cpu/ia64
-    ;;
   i[4567]86 | x86_64)
     atomic_flags="-march=native"
     ;;
-  powerpc* | rs6000)
-    atomic_word_dir=cpu/powerpc
-    ;;
   sparc* | ultrasparc)
     atomic_word_dir=cpu/sparc
     atomic_flags="-mcpu=v9"
@@ -226,12 +217,10 @@ case "${host_os}" in
     # explicitly duplicate the directory for 4.[<3].
     os_include_dir="os/aix"
     atomicity_dir="os/aix"
-    atomic_word_dir="os/aix"
     ;;
   aix4.*)
     os_include_dir="os/generic"
     atomicity_dir="os/aix"
-    atomic_word_dir="os/aix"
     ;;
   aix*)
     os_include_dir="os/generic"