Avoid running dub recursively in pre-generate command, call D compiler directly

As we see spurious failures (version_.di not generated/importable) when
calling dub recursively.

The generate_version executable is built each time this way, not cached
by dub anymore, but it's built pretty quickly (0.5 secs with LDC on my
Linux x64 box, 0.3 secs with DMD).

Author: kinke

dub.sdl

@@ -7,7 +7,7 @@ libs "ssl" "crypto" platform="posix"
 configuration "library-autodetect" {
 	targetType "sourceLibrary"
 	excludedSourceFiles "source/deimos/openssl/applink.d"
-	preGenerateCommands `${DUB} scripts/generate_version.d` platform="posix"
+	preGenerateCommands `$DC -run scripts/generate_version.d` platform="posix"
 	versions `DeimosOpenSSLAutoDetect`
 }
 

scripts/generate_version.d

@@ -30,7 +30,7 @@ import std.string;
 import std.uni;
 
 // file full path is: $SOME_PATH/openssl/scripts/generate_version.d
-// We want: $SOME_PATH/openssl/deimos/openssl/
+// We want: $SOME_PATH/openssl/source/deimos/openssl/
 immutable TARGET_DIR_PATH = __FILE_FULL_PATH__
     .dirName.dirName.buildPath("source", "deimos", "openssl");