Fix .size longjmp in the linux port of jerry-libc

Fixing a typo, which resulted in an undefined (but harmless) symbol
in jerry-asm.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss [email protected]

Author: akosthekiss

jerry-libc/target/linux/jerry-asm.S

@@ -67,4 +67,4 @@ setjmp:
 .type longjmp, %function
 longjmp:
   _LONGJMP
-.size longjmu, . - setjmp
+.size longjmp, . - setjmp