powi: don't override arm calling convention

Author: TimNN

Diff for: lib/builtins/powidf2.c

@@ -16,7 +16,7 @@
 
 /* Returns: a ^ b */
 
-COMPILER_RT_ABI double
+double
 __powidf2(double a, si_int b)
 {
     const int recip = b < 0;

Diff for: lib/builtins/powisf2.c

@@ -16,7 +16,7 @@
 
 /* Returns: a ^ b */
 
-COMPILER_RT_ABI float
+float
 __powisf2(float a, si_int b)
 {
     const int recip = b < 0;