fbc: In macro/define's use '##_' to escape line continuation character '_'

- allow multiple lines of macro expanded code to be combined into a single statement.(Skyfish)

Author: jayrm

changelog.txt

@@ -86,6 +86,7 @@ Version 1.08.0
 - added warning 'FOR counter variable is unable to exceed limit value' on constant end value for loops to help avoid infinite loops, e.g. for i as ubyte = 0 to 255
 - internal rtlib function fb_LEFTSELF( string, n ) to reduce the size of a string without reallocating the buffer
 - added GFX_SCREEN_EXIT = &h80000000l constant to fbgfx.bi - used with Screen 0 (closing any graphics window and preserving the console window content)
+- github #309: In macro/define's use '##_' to escape line continuation character '_' to allow multiple lines of macro expanded code to be combined into a single statement.(Skyfish)
 
 [fixed]
 - makefile: under MSYS2 (and friends), TARGET_ARCH is now identified from shell's default target architecture instead of shell's host architecture