Patch rdmd to auto-detect available *dmd binary

PKGBUILD

@@ -2,7 +2,7 @@
 
 pkgname=('dtools')
 pkgver=2.067.0
-pkgrel=1
+pkgrel=2
 pkgdesc="Ancilliary tools for the D programming language"
 license=("custom")
 groups=('dlang')
@@ -17,11 +17,13 @@ source=(
     "git+http://github.com/D-Programming-Language/tools#tag=v$pkgver"
     "git+https://github.com/Dicebot/Arch-PKGBUILDs.git"
     "http://www.boost.org/LICENSE_1_0.txt"
+    "autodetect.diff"
 )
 sha1sums=(
     'SKIP'
     'SKIP'
     '3cba29011be2b9d59f6204d6fa0a386b1b2dbd90'
+    '7fb5bd71d6c4e90c0ca49b292454e11169afdee8'
 )
 
 build()
@@ -30,6 +32,7 @@ build()
     DMD=ldmd
 
     cd $srcdir/tools
+    git apply $srcdir/autodetect.diff
 
     # rdmd is used to build others
     $DMD -od. -ofdtools-rdmd rdmd.d

autodetect.diff

@@ -0,0 +1,47 @@
+diff --git a/rdmd.d b/rdmd.d
+index 5d66c9f..61fb86a 100644
+--- a/rdmd.d
++++ b/rdmd.d
+@@ -51,7 +51,32 @@ else version (LDC)
+ else
+     static assert(false, "Unknown compiler");
+ 
+-private string compiler = defaultCompiler;
++private string compiler;
++
++void chooseCompiler(ref string compiler)
++{
++    import std.stdio;
++
++    // if compiler is set explicitly, don't interefer
++    // otherwise find one that exists in PATH
++    if (!compiler.length)
++    {
++        import std.process : executeShell;
++        auto compilers = [ defaultCompiler, "dmd", "ldmd2", "gdmd2", "ldmd", "gdmd" ];   
++
++        foreach (candidate; compilers)
++        {
++            // dirty hack, no-arg dmd invocation will return 1
++            if (executeShell(candidate ~ "| grep Usage").status == 0)
++            {
++                compiler = candidate;
++                return;
++            }
++        }
++
++        throw new Exception("Couldn't find any D compiler");
++    }
++}
+ 
+ int main(string[] args)
+ {
+@@ -141,6 +166,8 @@ int main(string[] args)
+     if (bailout) return 0;
+     if (dryRun) chatty = true; // dry-run implies chatty
+ 
++    chooseCompiler(compiler);
++
+     /* Only -of is supported because Make is very susceptible to file names, and
+      * it doesn't do a good job resolving them. One option would be to use
+      * std.path.buildNormalizedPath(), but some corner cases will break, so it