cvise: explicitly point to clang-format

Without the cnage `cvise` fails to normalize sources with
`clang-format` and produces less than ideal intermediate sources to
lines-based pass. That affects reduction speed among other things.

Before the change `cvise` complained as:

    $ cvise --command 'grep foo a.c' a.c
    00:00:00 INFO Using temporary interestingness test: /tmp/tmp4a_4wut0.sh
    00:00:00 ERROR cannot find external program clang-format
    00:00:00 ERROR Prereqs not found for pass IndentPass::regular

After the change `clang-format` is found:

    $ result/bin/cvise --command 'grep foo a.c' a.c
    00:00:00 INFO Using temporary interestingness test: /tmp/tmpudipespb.sh
    00:00:00 INFO ===< 1539388 >===

While at it used `--replace-fail`.

pkgs/development/tools/misc/cvise/default.nix

@@ -1,6 +1,7 @@
 { lib
 , buildPythonApplication
 , fetchFromGitHub
+, clang-tools
 , cmake
 , colordiff
 , flex
@@ -34,11 +35,11 @@ buildPythonApplication rec {
     # Avoid blanket -Werror to evade build failures on less
     # tested compilers.
     substituteInPlace CMakeLists.txt \
-      --replace " -Werror " " "
+      --replace-fail " -Werror " " "
 
     substituteInPlace cvise/utils/testing.py \
-      --replace "'colordiff --version'" "'${colordiff}/bin/colordiff --version'" \
-      --replace "'colordiff'" "'${colordiff}/bin/colordiff'"
+      --replace-fail "'colordiff --version'" "'${colordiff}/bin/colordiff --version'" \
+      --replace-fail "'colordiff'" "'${colordiff}/bin/colordiff'"
   '';
 
   nativeBuildInputs = [
@@ -65,6 +66,12 @@ buildPythonApplication rec {
     unifdef
   ];
 
+  cmakeFlags = [
+    # By default `cvise` looks it up in `llvm` bin directory. But
+    # `nixpkgs` moves it into a separate derivation.
+    "-DCLANG_FORMAT_PATH=${clang-tools}/bin/clang-format"
+  ];
+
   disabledTests = [
     # Needs gcc, fails when run noninteractively (without tty).
     "test_simple_reduction"