Taken from the Gentoo patch:
https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-devel/llvm-roc/files/llvm-roc-5.0.0-linkdl.patch

LLVMOffloadArch should link libdl to fix undefined symbol 'dlsym' when linking

--- a/llvm/lib/OffloadArch/offload-arch/CMakeLists.txt
+++ b/llvm/lib/OffloadArch/offload-arch/CMakeLists.txt
@@ -3,6 +3,7 @@ add_llvm_tool(offload-arch
   ${CMAKE_CURRENT_SOURCE_DIR}/offload-arch.cpp
   DEPENDS generated-table LLVMOffloadArch
 )
+target_link_libraries(LLVMOffloadArch PRIVATE ${CMAKE_DL_LIBS})
 target_link_libraries(offload-arch PRIVATE LLVMOffloadArch)
 
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<tr><td><span title='2018-02-26 20:58:14 +0100'>2018-02-26</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=6d796220c417a34100c282a7fa1f9afb6ac00339'>gnu: ninja: Patch /bin/echo in the correct file.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2018-02-26 20:37:04 +0100'>2018-02-26</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=d0de4c40e24ee52e4382ee2ac82088932ab49099'>gnu: ninja: Patch hard-coded /bin/echo reference.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2018-01-19 13:19:33 +0100'>2018-01-19</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=5bb12e1462c4ecfbed829b09ed011853dd74209d'>gnu: ninja: Update to 1.8.2.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-03-17 20:41:15 +0100'>2017-03-17</span></td><td><a href='/guix/commit/gnu/packages/ninja.scm?id=cbef2796edcd35d63fd5a1eea9390fc98564c7f2'>gnu: ninja: Update to 1.7.2.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>