build.d: Use pragmas to detect host compiler

Less brittle than parsing the output of --version
(especially to determine the frontend version)

src/build.d

@@ -991,21 +991,24 @@ void processEnvironment()
 
  const os = env["OS"];
 
- const hostDMDVersion = [env["HOST_DMD_RUN"], "--version"].execute.output;
-
- alias DMD = AliasSeq!("DMD");
- alias LDC = AliasSeq!("LDC");
- alias GDC = AliasSeq!("GDC", "gdmd", "gdc");
- const kindIdx = hostDMDVersion.canFind(DMD, LDC, GDC);
-
- enforce(kindIdx, "Invalid Host DMD found: " ~ hostDMDVersion);
-
- if (kindIdx <= DMD.length)
- env["HOST_DMD_KIND"] = "dmd";
- else if (kindIdx <= LDC.length + DMD.length)
- env["HOST_DMD_KIND"] = "ldc";
- else
- env["HOST_DMD_KIND"] = "gdc";
+ // Detect the host compiler kind and version
+ with (pipeProcess([env["HOST_DMD_RUN"], "-c", "-o-", "-"]))
+ {
+ stdin.writeln(q{
+ pragma(msg, __VENDOR__);
+ pragma(msg, __VERSION__);
+ });
+ stdin.close();
+ pid.wait();
+ const vendor = stderr.readln().strip();
+
+ env["HOST_DMD_KIND"] = [
+ "Digital Mars D": "dmd",
+ "LDC": "ldc",
+ "GNU D": "gdc"
+ ][vendor];
+ env["HOST_DMD_VERSION"] = stderr.readln().strip()[0 .. $ - 1]; // Remove L
+ }
 
  env["DMD_PATH"] = env["G"].buildPath("dmd").exeName;
  env.getDefault("DETAB", "detab");