[turbofan] Add CalleeSavedFPRegisters to CallDescriptor.

src/compiler/arm/linkage-arm.cc

Index: src/compiler/arm/linkage-arm.cc
diff --git a/src/compiler/arm/linkage-arm.cc b/src/compiler/arm/linkage-arm.cc
index 2b1faa2aca27ba3aa2b6fc86f3710532fd8f5e58..b791e41e022b77a1343ea5e4ae3f6f27837d1941 100644
--- a/src/compiler/arm/linkage-arm.cc
+++ b/src/compiler/arm/linkage-arm.cc
@@ -23,6 +23,10 @@ struct ArmLinkageHelperTraits {
     return r4.bit() | r5.bit() | r6.bit() | r7.bit() | r8.bit() | r9.bit() |
            r10.bit();
   }
+  static RegList CCalleeSaveFPURegisters() {

[paul.l..., 2015/06/15 23:05:16]

We should not use FPU in the names, that is MIPS specific. I first was thinking
CCalleeSaveDoubleRegisters(), as that is very generic. However, arm64 uses 'FP',
and I like that, plus the names don't get insanely long:
CCalleeSaveFPRegisters()

[akos.palfi.imgtec, 2015/06/22 17:33:20]

Done.

+    // TODO(palfia): finish.
+    return 0;
+  }
   static Register CRegisterParameter(int i) {
     static Register register_parameters[] = {r0, r1, r2, r3};
     return register_parameters[i];