Fix makefile in MultiSource/UnitTests/Float (#113)

"Makefile:9: *** invalid syntax in conditional.  Stop."
The error occurred and I fixed it.
diff --git a/MultiSource/UnitTests/Float/Makefile b/MultiSource/UnitTests/Float/Makefile
index 8fa46ea..6edd680 100644
--- a/MultiSource/UnitTests/Float/Makefile
+++ b/MultiSource/UnitTests/Float/Makefile
@@ -6,7 +6,7 @@
 
 # Tests in 'rounding' can run only if the target implements builtin functions
 # for rounding mode manipulation.
-ifneq (, $filter($(ARCH), X86_64 AArch64)
+ifneq (,$(filter $(ARCH), X86_64 AArch64))
 PARALLEL_DIRS += rounding
 endif