gcc: support avr

- respect libc’s incdir and libdir
- make non-unix systems single threaded
- set LIMITS_H_TEST to false for avr
- misc updates to support new libc’s
- use multilib with avr

For threads we want to use:
- posix on unix systems
- win32 on windows
- single on everything else

For avr:
- add library directories for avrlibc
- to disable relro and bind
- avr5 should have precedence over avr3 - otherwise gcc uses the wrong one

pkgs/development/compilers/gcc/4.9/default.nix

@@ -135,7 +135,7 @@ let version = "4.9.4";
         "--disable-libmpx" # requires libc
       ] else [
         (if crossDarwin then "--with-sysroot=${getLib libcCross}/share/sysroot"
-         else                "--with-headers=${getDev libcCross}/include")
+         else                "--with-headers=${getDev libcCross}${libcCross.incdir or "/include"}")
         "--enable-__cxa_atexit"
         "--enable-long-long"
       ] ++
@@ -156,10 +156,15 @@ let version = "4.9.4";
             # In uclibc cases, libgomp needs an additional '-ldl'
             # and as I don't know how to pass it, I disable libgomp.
             "--disable-libgomp"
-          ] ++ [
-          "--enable-threads=posix"
-          "--enable-nls"
-          "--disable-decimal-float" # No final libdecnumber (it may work only in 386)
+          ]
+          ++ optional (targetPlatform.libc == "newlib") "--with-newlib"
+          ++ optional (targetPlatform.libc == "avrlibc") "--with-avrlibc"
+          ++ [
+            "--enable-threads=${if targetPlatform.isUnix then "posix"
+                                else if targetPlatform.isWindows then "win32"
+                                else "single"}"
+            "--enable-nls"
+            "--disable-decimal-float" # No final libdecnumber (it may work only in 386)
         ]));
     stageNameAddon = if crossStageStatic then "-stage-static" else "-stage-final";
     crossNameAddon = if targetPlatform != hostPlatform then "${targetPlatform.config}${stageNameAddon}-" else "";
@@ -292,7 +297,7 @@ stdenv.mkDerivation ({
       }"
     ] ++
 
-    (if enableMultilib
+    (if (enableMultilib || targetPlatform.isAvr)
       then ["--enable-multilib" "--disable-libquadmath"]
       else ["--disable-multilib"]) ++
     optional (!enableShared) "--disable-shared" ++
@@ -381,20 +386,20 @@ stdenv.mkDerivation ({
   EXTRA_TARGET_FLAGS = optionals
     (targetPlatform != hostPlatform && libcCross != null)
     ([
-      "-idirafter ${getDev libcCross}/include"
+      "-idirafter ${getDev libcCross}${libcCross.incdir or "/include"}"
     ] ++ optionals (! crossStageStatic) [
-      "-B${libcCross.out}/lib"
+      "-B${libcCross.out}${libcCross.libdir or "/lib"}"
     ]);
 
   EXTRA_TARGET_LDFLAGS = optionals
     (targetPlatform != hostPlatform && libcCross != null)
     ([
-      "-Wl,-L${libcCross.out}/lib"
+      "-Wl,-L${libcCross.out}${libcCross.libdir or "/lib"}"
     ] ++ (if crossStageStatic then [
-        "-B${libcCross.out}/lib"
+        "-B${libcCross.out}${libcCross.libdir or "/lib"}"
       ] else [
-        "-Wl,-rpath,${libcCross.out}/lib"
-        "-Wl,-rpath-link,${libcCross.out}/lib"
+        "-Wl,-rpath,${libcCross.out}${libcCross.libdir or "/lib"}"
+        "-Wl,-rpath-link,${libcCross.out}${libcCross.libdir or "/lib"}"
     ]));
 
   passthru =