fix: use explicit import in PPC/CodeGen.hs to avoid ambiguity

The GADT refactoring of Reg/Target exports RegOps(..) which includes
mkVirtualReg as a typeclass method. PPC/CodeGen.hs imports both PPC.Regs
(which has its own mkVirtualReg) and Reg.Target, creating an ambiguous
reference.

Fix by using an explicit import list for Reg.Target, importing only
targetClassOfReg which is the only function actually used.

Author: angerman

compiler/GHC/CmmToAsm/PPC/CodeGen.hs

@@ -43,7 +43,7 @@ import GHC.CmmToAsm.Format
 import GHC.CmmToAsm.Config
 import GHC.Platform.Reg.Class.Unified
 import GHC.Platform.Reg
-import GHC.CmmToAsm.Reg.Target
+import GHC.CmmToAsm.Reg.Target (targetClassOfReg)
 import GHC.Platform
 
 -- Our intermediate code: