use macro instead of attributes for weak aliases.

src/system/libroot/posix/arch/x86/fenv.c

@@ -207,5 +207,5 @@ __fedisableexcept(int mask)
 	return (~omask);
 }
 
-int feenableexcept(int) __attribute__((weak, alias("__feenableexcept")));
-int fedisableexcept(int) __attribute__((weak, alias("__fedisableexcept")));
+__weak_reference(__feenableexcept, feenableexcept);
+__weak_reference(__fedisableexcept, fedisableexcept);

src/system/libroot/posix/glibc/arch/generic/w_dremf.c

@@ -13,5 +13,5 @@ __dremf(float x, float y)
 {
 	return __remainderf(x, y);
 }
+weak_alias (__dremf, dremf)
 
-float dremf(float, float) __attribute__((weak, alias("__dremf")));