Simplify library logic on MacOS (#59)

As suggested by @giordano #58 (comment)

Author: simonbyrne

src/Quadmath.jl

@@ -21,11 +21,12 @@ import Base: (*), +, -, /,  <, <=, ==, ^, convert,
 
 using Random
 
-if Sys.isapple() && Sys.ARCH == :x86_64
-    const quadoplib = "libgcc_s.1.dylib"
-    const libquadmath = "libquadmath.0"
-elseif Sys.isapple() && Sys.ARCH == :aarch64
-    const quadoplib = "libgcc_s.1.1.dylib"
+if Sys.isapple()
+    if Sys.ARCH == :x86_64
+        const quadoplib = "libgcc_s.1.dylib"
+    elseif Sys.ARCH == :aarch64
+        const quadoplib = "libgcc_s.1.1.dylib"
+    end
     const libquadmath = "libquadmath.0"
 elseif Sys.isunix()
     const quadoplib = "libgcc_s.so.1"