fix src/filters/2xSaImmx.asm linking issues #98

Because of how asm subroutines are linked to C/C++ programs,
src/filters/2xSaImmx.asm had an %ifdef __DJGPP__ (the DOS port of gcc)
with the subroutine names prepended with an extra underscore.

In 902a7a7e I removed the %ifdef and just kept the extra underscore for
all symbols, and this worked fine until #98 where some version of Fedora
did not like that and would not link the code.

So adopt the behavior of the other asm filters, which have a NEWSYM
macro that defines the symbol name both with and without the extra
underscore, by listing the symbol twice, both with and without the extra
underscore, this is confirmed to fix the linking issue on that Fedora
build host.

src/filters/2xSaImmx.asm

@@ -31,6 +31,11 @@ GLOBAL __2xSaILine
 GLOBAL __2xSaISuperEagleLine
 GLOBAL __2xSaISuper2xSaILine
 GLOBAL _Init_2xSaIMMX
+
+GLOBAL _2xSaILine
+GLOBAL _2xSaISuperEagleLine
+GLOBAL _2xSaISuper2xSaILine
+GLOBAL Init_2xSaIMMX
 SECTION .text ALIGN = 32
 
 %ifdef FAR_POINTER
@@ -80,6 +85,7 @@ colorA3   equ 4
 
 
 __2xSaISuper2xSaILine:
+_2xSaISuper2xSaILine:
 ; Store some stuff
          push ebp
          mov ebp, esp
@@ -815,6 +821,7 @@ __2xSaISuper2xSaILine:
 
 
 __2xSaISuperEagleLine:
+_2xSaISuperEagleLine:
 ; Store some stuff
          push ebp
          mov ebp, esp
@@ -1391,6 +1398,7 @@ colorO   equ 2
 colorP   equ 4
 
 __2xSaILine:
+_2xSaILine:
 ; Store some stuff
          push ebp
          mov ebp, esp
@@ -1978,6 +1986,7 @@ __2xSaILine:
 ;-------------------------------------------------------------------------
 
 _Init_2xSaIMMX:
+Init_2xSaIMMX:
 ; Store some stuff
          push ebp
          mov ebp, esp