Don't wastefully execute everything via a shell

We should only ever use the shell if we want to use the shell's
features, such as pipes, non-trivial redirection, or shell language
features (branches/loops/etc.).  Otherwise, executing a program via
the shell is pointless and wasteful.

source/dub/compilers/compiler.d

@@ -152,12 +152,12 @@ interface Compiler {
 
 		int status;
 		if (output_callback) {
-			auto result = executeShell(escapeShellCommand(args),
+			auto result = execute(args,
 				env, Config.none, size_t.max, cwd.toNativeString());
 			output_callback(result.status, result.output);
 			status = result.status;
 		} else {
-			auto compiler_pid = spawnShell(escapeShellCommand(args),
+			auto compiler_pid = spawnProcess(args,
 				env, Config.none, cwd.toNativeString());
 			status = compiler_pid.wait();
 		}
@@ -185,7 +185,7 @@ interface Compiler {
 
 		auto fil = generatePlatformProbeFile();
 
-		auto result = executeShell(escapeShellCommand(compiler_binary ~ args ~ fil.toNativeString()));
+		auto result = execute(compiler_binary ~ args ~ fil.toNativeString());
 		enforce!CompilerInvocationException(result.status == 0,
 				format("Failed to invoke the compiler %s to determine the build platform: %s",
 				compiler_binary, result.output));

source/dub/internal/git.d

@@ -72,7 +72,7 @@ private string determineVersionWithGitTool(NativePath path)
 	auto git_dir_param = "--git-dir=" ~ git_dir.toNativeString();
 
 	static string exec(scope string[] params...) {
-		auto ret = executeShell(escapeShellCommand(params));
+		auto ret = execute(params);
 		if (ret.status == 0) return ret.output.strip;
 		logDebug("'%s' failed with exit code %s: %s", params.join(" "), ret.status, ret.output.strip);
 		return null;