[libc] Refactor stdfix extension from llvm_libc_ext.td to llvm_libc_stdfix_ext.td. (#84365)

This fixes runtime build for armv6 baremetal targets:
#83959 (comment)

Author: lntue

libc/config/baremetal/api.td

@@ -2,7 +2,7 @@ include "config/public_api.td"
 
 include "spec/stdc.td"
 include "spec/stdc_ext.td"
-include "spec/llvm_libc_ext.td"
+include "spec/llvm_libc_stdfix_ext.td"
 
 def AssertMacro : MacroDef<"assert"> {
   let Defn = [{

libc/config/linux/api.td

@@ -7,6 +7,7 @@ include "spec/gnu_ext.td"
 include "spec/bsd_ext.td"
 include "spec/stdc_ext.td"
 include "spec/llvm_libc_ext.td"
+include "spec/llvm_libc_stdfix_ext.td"
 
 def AssertMacro : MacroDef<"assert"> {
   let Defn = [{

libc/spec/llvm_libc_ext.td

@@ -51,29 +51,9 @@ def LLVMLibcExt : StandardSpec<"llvm_libc_ext"> {
       ]
   >;
 
-  HeaderSpec StdFix = HeaderSpec<
-      "stdfix.h",
-      [],  // macros
-      [],  // types
-      [],  // enums
-      [    // functions
-          GuardedFunctionSpec<"sqrtuhr", RetValSpec<UnsignedShortFractType>, [ArgSpec<UnsignedShortFractType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-          GuardedFunctionSpec<"sqrtur", RetValSpec<UnsignedFractType>, [ArgSpec<UnsignedFractType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-          GuardedFunctionSpec<"sqrtulr", RetValSpec<UnsignedLongFractType>, [ArgSpec<UnsignedLongFractType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-
-          GuardedFunctionSpec<"sqrtuhk", RetValSpec<UnsignedShortAccumType>, [ArgSpec<UnsignedShortAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-          GuardedFunctionSpec<"sqrtuk", RetValSpec<UnsignedAccumType>, [ArgSpec<UnsignedAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-          GuardedFunctionSpec<"sqrtulk", RetValSpec<UnsignedLongAccumType>, [ArgSpec<UnsignedLongAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-
-          GuardedFunctionSpec<"uhksqrtus", RetValSpec<UnsignedShortAccumType>, [ArgSpec<UnsignedShortType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-          GuardedFunctionSpec<"uksqrtui", RetValSpec<UnsignedAccumType>, [ArgSpec<UnsignedIntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
-      ]
-  >;
-
   let Headers = [
     Assert,
     Sched,
-    StdFix,
     Strings,
   ];
 }

libc/spec/llvm_libc_stdfix_ext.td

@@ -0,0 +1,24 @@
+def LLVMLibcStdfixExt : StandardSpec<"llvm_libc_stdfix_ext"> {
+  HeaderSpec StdFix = HeaderSpec<
+      "stdfix.h",
+      [],  // macros
+      [],  // types
+      [],  // enums
+      [    // functions
+          GuardedFunctionSpec<"sqrtuhr", RetValSpec<UnsignedShortFractType>, [ArgSpec<UnsignedShortFractType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"sqrtur", RetValSpec<UnsignedFractType>, [ArgSpec<UnsignedFractType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"sqrtulr", RetValSpec<UnsignedLongFractType>, [ArgSpec<UnsignedLongFractType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+
+          GuardedFunctionSpec<"sqrtuhk", RetValSpec<UnsignedShortAccumType>, [ArgSpec<UnsignedShortAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"sqrtuk", RetValSpec<UnsignedAccumType>, [ArgSpec<UnsignedAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"sqrtulk", RetValSpec<UnsignedLongAccumType>, [ArgSpec<UnsignedLongAccumType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+
+          GuardedFunctionSpec<"uhksqrtus", RetValSpec<UnsignedShortAccumType>, [ArgSpec<UnsignedShortType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+          GuardedFunctionSpec<"uksqrtui", RetValSpec<UnsignedAccumType>, [ArgSpec<UnsignedIntType>], "LIBC_COMPILER_HAS_FIXED_POINT">,
+      ]
+  >;
+
+  let Headers = [
+    StdFix,
+  ];
+}