gnu: nextpnr-ice40: Update to 0.8.

* gnu/packages/fpga.scm (nextpnr-ice40): Update to 0.8.
[snippet]: Use 'delete-all-but' defensive idiom and update comment.
[patches]: Apply unbundling patches.
[arguments] <:cmake>: New argument.
<#:configure-flags>: Add -DUSE_OPENMP=ON flag.  Adjust version string used with
-DCURRENT_GIT_VERSION.
<#:phases> {patch-source}: Streamline phase.
[inputs]: Remove imgui-1.86, which is now propagated by qtimgui.
[home-page]: Add trailing '/'.
[description]: Streamline description.  'FOSS' is implied by being part of the
Guix packages collection.
[license]: Correct to ISC license.
* gnu/packages/patches/nextpnr-gtest.patch: New file.
* gnu/packages/patches/nextpnr-imgui.patch: Likewise.
* gnu/local.mk (dist_patch_DATA): Register them.

Co-authored-by: Cayetano Santos <csantosb@inventati.org>
Change-Id: Ied1178c26ed0ba96021a3d5961441c23f0ac508e

gnu/packages/patches/nextpnr-gtest.patch

@@ -0,0 +1,30 @@
+Upstream-status: https://github.com/YosysHQ/nextpnr/pull/1478
+
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 47d60330..88463984 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -217,7 +217,13 @@ set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/3rdparty/sanitizers-cmake/cmake" ${CM
+ find_package(Sanitizers)
+ 
+ if (BUILD_TESTS)
+-    add_subdirectory(3rdparty/googletest/googletest EXCLUDE_FROM_ALL)
++    find_package(GTest)
++    if(GTest_FOUND)
++        add_library(gtest_main ALIAS GTest::gtest_main)
++    else()
++        add_subdirectory(3rdparty/googletest/googletest EXCLUDE_FROM_ALL)
++        set(gtest_include_dir ${CMAKE_SOURCE_DIR}/3rdparty/googletest/googletest/include)
++    endif()
+     enable_testing()
+ endif()
+ 
+@@ -366,7 +372,7 @@ function(add_nextpnr_architecture target)
+         add_executable(nextpnr-${target}-test ${arg_TEST_SOURCES})
+         set_property(TARGET nextpnr-${target}-test PROPERTY RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})
+ 
+-        target_include_directories(nextpnr-${target}-test PRIVATE ${CMAKE_SOURCE_DIR}/3rdparty/googletest/googletest/include)
++        target_include_directories(nextpnr-${target}-test PRIVATE gtest_include_dir)
+ 
+         target_link_libraries(nextpnr-${target}-test PRIVATE gtest_main nextpnr-${target}-core)
+         if (BUILD_GUI)