swift: 4.2.3 -> 5.0.1

update Swift
* new tweaks to the build process are mostly documented inline
* the swiftc wrapper needs the linker path for libicu
* some older tweaks could be removed
* remove fuzz from patches by updating line numbers
* one build fix to libdispatch has been filed upstream

pkgs/development/compilers/swift/patches/0001-build-presets-linux-don-t-require-using-Ninja.patch

@@ -11,8 +11,8 @@ diff --git a/utils/build-presets.ini b/utils/build-presets.ini
 index 7ee57ad2df..e6b0af3581 100644
 --- a/utils/build-presets.ini
 +++ b/utils/build-presets.ini
-@@ -717,7 +717,7 @@ swiftpm
- xctest
+@@ -721,7 +721,7 @@ swiftpm
+ 
  dash-dash
  
 -build-ninja