fix aliases not using underscore prefixes in assembler code

long double functions, that are identical to double functions, usually
define themselves as weak references to their double counterpart.
However, the piece of assembler written for that produces

  .equ <name>l, <name>

but on SuperH C-exported symbols have leading underscores. This commit
adds an SH3 exception to use instead

  .equ _<name>l, _<name>

which fixes a number of long double functions.

src/cdefs-compat.h

@@ -34,9 +34,15 @@
 #else
 #ifdef __ELF__
 #ifdef __STDC__
+#if defined(__sh3__)
+#define openlibm_weak_reference(sym,alias)	\
+	__asm__(".weak _" #alias);	\
+	__asm__(".equ _" #alias ", _" #sym)
+#else
 #define openlibm_weak_reference(sym,alias)	\
 	__asm__(".weak " #alias);	\
 	__asm__(".equ "  #alias ", " #sym)
+#endif /* __sh3__ */
 #ifdef __warn_references
 #define openlibm_warn_references(sym,msg) __warn_references(sym,msg)
 #else