Don't depend on string.h in codegen (#8299)

compiler/cgen.nim

@@ -80,11 +80,6 @@ proc isSimpleConst(typ: PType): bool =
       {tyTuple, tyObject, tyArray, tySet, tySequence} and not
       (t.kind == tyProc and t.callConv == ccClosure)
 
-proc useStringh(m: BModule) =
-  if includesStringh notin m.flags:
-    incl m.flags, includesStringh
-    m.includeHeader("<string.h>")
-
 proc useHeader(m: BModule, sym: PSym) =
   if lfHeader in sym.loc.flags:
     assert(sym.annex != nil)
@@ -320,10 +315,9 @@ proc resetLoc(p: BProc, loc: var TLoc) =
       # field, so disabling this should be safe:
       genObjectInit(p, cpsStmts, loc.t, loc, true)
     else:
-      useStringh(p.module)
       # array passed as argument decayed into pointer, bug #7332
       # so we use getTypeDesc here rather than rdLoc(loc)
-      linefmt(p, cpsStmts, "memset((void*)$1, 0, sizeof($2));$n",
+      linefmt(p, cpsStmts, "#nimZeroMem((void*)$1, sizeof($2));$n",
               addrLoc(p.config, loc), getTypeDesc(p.module, loc.t))
       # XXX: We can be extra clever here and call memset only
       # on the bytes following the m_type field?
@@ -336,11 +330,10 @@ proc constructLoc(p: BProc, loc: TLoc, isTemp = false) =
       getTypeDesc(p.module, typ))
   else:
     if not isTemp or containsGarbageCollectedRef(loc.t):
-      # don't use memset for temporary values for performance if we can
+      # don't use nimZeroMem for temporary values for performance if we can
       # avoid it:
       if not isImportedCppType(typ):
-        useStringh(p.module)
-        linefmt(p, cpsStmts, "memset((void*)$1, 0, sizeof($2));$n",
+        linefmt(p, cpsStmts, "#nimZeroMem((void*)$1, sizeof($2));$n",
                 addrLoc(p.config, loc), getTypeDesc(p.module, typ))
     genObjectInit(p, cpsStmts, loc.t, loc, true)