gnu: Add llvm-for-rocm.

* gnu/packages/rocm.scm (llvm-for-rocm): New variable.
* gnu/packages/patches/llvm-roc-3.0.0-add_libraries.patch,
gnu/packages/patches/llvm-roc-4.0.0-remove-isystem-usr-include.patch,
gnu/packages/patches/llvm-roc-4.2.0-add_Object.patch: New files.
* gnu/local.mk (dist_patch_DATA): Add them.

gnu/local.mk

@@ -1416,6 +1416,9 @@ dist_patch_DATA =						\
   %D%/packages/patches/llvm-9-fix-bitcast-miscompilation.patch	\
   %D%/packages/patches/llvm-9-fix-lpad-miscompilation.patch	\
   %D%/packages/patches/llvm-9-fix-scev-miscompilation.patch	\
+  %D%/packages/patches/llvm-roc-3.0.0-add_libraries.patch \
+  %D%/packages/patches/llvm-roc-4.0.0-remove-isystem-usr-include.patch \
+  %D%/packages/patches/llvm-roc-4.2.0-add_Object.patch \
   %D%/packages/patches/lm-sensors-hwmon-attrs.patch		\
   %D%/packages/patches/lrcalc-includes.patch    		\
   %D%/packages/patches/lsh-fix-x11-forwarding.patch		\

gnu/packages/patches/llvm-roc-3.0.0-add_libraries.patch

@@ -0,0 +1,22 @@
+Taken from https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-devel/llvm-roc/files
+
+diff -Naur a/clang/lib/Basic/CMakeLists.txt b/clang/lib/Basic/CMakeLists.txt
+--- a/clang/lib/Basic/CMakeLists.txt	2019-12-28 07:42:49.119055933 +0100
++++ b/clang/lib/Basic/CMakeLists.txt	2019-12-28 07:42:13.265056070 +0100
+@@ -2,6 +2,7 @@
+   Core
+   MC
+   Support
++  Option
+   )
+ 
+ find_first_existing_vc_file("${LLVM_MAIN_SRC_DIR}" llvm_vc)
+diff -Naur a/clang/lib/Driver/CMakeLists.txt b/clang/lib/Driver/CMakeLists.txt
+--- a/clang/lib/Driver/CMakeLists.txt	2019-12-28 07:41:39.521056199 +0100
++++ b/clang/lib/Driver/CMakeLists.txt	2019-12-28 07:40:23.998056487 +0100
+@@ -79,4 +79,5 @@
+   LINK_LIBS
+   clangBasic
+   ${system_libs}
++  pthread
+   )

gnu/packages/patches/llvm-roc-4.0.0-remove-isystem-usr-include.patch

@@ -0,0 +1,29 @@
+Author: Wilfried (justxi) Holzke
+
+Adopted from https://github.com/justxi/rocm/blob/master/sys-devel/llvm-roc/files/llvm-roc-4.0.0-remove-isystem-usr-include.patch
+
+Index: llvm-project-rocm-4.0.0/clang/lib/Driver/ToolChains/AMDGPU.cpp
+===================================================================
+--- llvm-project-rocm-4.0.0.orig/clang/lib/Driver/ToolChains/AMDGPU.cpp
++++ llvm-project-rocm-4.0.0/clang/lib/Driver/ToolChains/AMDGPU.cpp
+@@ -326,11 +326,6 @@ void RocmInstallationDetector::AddHIPInc
+     //
+     // ROCm 3.5 does not fully support the wrapper headers. Therefore it needs
+     // a workaround.
+-    SmallString<128> P(D.ResourceDir);
+-    if (UsesRuntimeWrapper)
+-      llvm::sys::path::append(P, "include", "cuda_wrappers");
+-    CC1Args.push_back("-internal-isystem");
+-    CC1Args.push_back(DriverArgs.MakeArgString(P));
+   }
+ 
+   if (DriverArgs.hasArg(options::OPT_nogpuinc))
+@@ -341,8 +336,6 @@ void RocmInstallationDetector::AddHIPInc
+     return;
+   }
+ 
+-  CC1Args.push_back("-internal-isystem");
+-  CC1Args.push_back(DriverArgs.MakeArgString(getIncludePath()));
+   if (UsesRuntimeWrapper)
+     CC1Args.append({"-include", "__clang_hip_runtime_wrapper.h"});
+ }

gnu/packages/patches/llvm-roc-4.2.0-add_Object.patch

@@ -0,0 +1,13 @@
+Taken from https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-devel/llvm-roc/files
+
+diff --color -uprN orig/lib/Target/AMDGPU/Disassembler/CMakeLists.txt llvm/lib/Target/AMDGPU/Disassembler/CMakeLists.txt
+--- a/llvm/lib/Target/AMDGPU/Disassembler/CMakeLists.txt	2021-06-14 11:57:54.222796911 +0800
++++ b/llvm/lib/Target/AMDGPU/Disassembler/CMakeLists.txt	2021-06-14 11:58:35.206796875 +0800
+@@ -11,6 +11,7 @@ add_llvm_component_library(LLVMAMDGPUDis
+   MC
+   MCDisassembler
+   Support
++  Object
+ 
+   ADD_TO_COMPONENT
+   AMDGPU

gnu/packages/rocm.scm

@@ -55,3 +55,38 @@ (define-public rocm-cmake
     (description "ROCm cmake modules provides cmake modules for common build
 tasks needed for the ROCM software stack.")
     (license license:ncsa)))
+
+(define-public llvm-for-rocm
+  (hidden-package
+   (package
+     ;; Actually based on LLVM 13 as of v4.3, but llvm-12 works just fine.
+     (inherit llvm-12)
+     (name "llvm-for-rocm")
+     (version %rocm-version)
+     (source (origin
+               (method git-fetch)
+               (uri (git-reference
+                     (url "https://github.com/RadeonOpenCompute/llvm-project.git")
+                     (commit (string-append "rocm-" version))))
+               (file-name (git-file-name name version))
+               (sha256
+                (base32
+                 "0p75nr1qpmy6crymdax5hm40wkimman4lnglz4x5cnbiqindya7s"))
+               (patches
+                (search-patches "llvm-roc-4.2.0-add_Object.patch"
+                                "llvm-roc-3.0.0-add_libraries.patch"
+                                "llvm-roc-4.0.0-remove-isystem-usr-include.patch"))))
+     (arguments
+      (substitute-keyword-arguments (package-arguments llvm-12)
+        ((#:phases phases '%standard-phases)
+         `(modify-phases ,phases
+            (add-after 'unpack 'chdir
+              (lambda _
+                (chdir "llvm")))))
+        ((#:configure-flags flags)
+         ''("-DLLVM_ENABLE_PROJECTS=llvm;clang;lld"
+            "-DLLVM_TARGETS_TO_BUILD=AMDGPU;X86"
+            "-DCMAKE_SKIP_BUILD_RPATH=FALSE"
+            "-DCMAKE_BUILD_WITH_INSTALL_RPATH=FALSE"
+            "-DBUILD_SHARED_LIBS:BOOL=TRUE"
+            "-DLLVM_VERSION_SUFFIX=")))))))