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-imgui.patch

@@ -0,0 +1,75 @@
+Uptream-status: https://github.com/YosysHQ/nextpnr/pull/1480
+
+diff --git a/gui/CMakeLists.txt b/gui/CMakeLists.txt
+index ff5d9208..c554cc96 100644
+--- a/gui/CMakeLists.txt
++++ b/gui/CMakeLists.txt
+@@ -46,12 +46,42 @@ target_include_directories(nextpnr-${target}-gui PUBLIC
+     ${CMAKE_CURRENT_SOURCE_DIR}
+ )
+ 
++# Detect whether imgui/qtimgui packages are available from the system.
++find_path(IMGUI_INCLUDE_DIR NAMES imgui.h PATH_SUFFIXES imgui)
++find_path(QTIMGUI_INCLUDE_DIR NAMES QtImGui.h PATH_SUFFIXES qtimgui)
++find_library(IMGUI_LIB NAMES imgui)
++find_library(QTIMGUI_LIB NAMES qt_imgui_widgets)
++if (IMGUI_INCLUDE_DIR AND IMGUI_LIB)
++    message("Using system imgui library:
++    IMGUI_INCLUDE_DIR=${IMGUI_INCLUDE_DIR}
++    IMGUI_LIB=${IMGUI_LIB}")
++else()
++    message("Using bundled imgui library")
++    set(IMGUI_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/3rdparty/imgui)
++    set(IMGUI_SOURCES
++        ../3rdparty/imgui/imgui_widgets.cpp
++        ../3rdparty/imgui/imgui_draw.cpp
++        ../3rdparty/imgui/imgui.cpp
++        ../3rdparty/imgui/imgui_demo.cpp)
++endif()
++if (QTIMGUI_INCLUDE_DIR AND QTIMGUI_LIB)
++    message("Using system qtimgui library:
++    QTIMGUI_INCLUDE_DIR=${QTIMGUI_INCLUDE_DIR}
++    QTIMGUI_LIB=${QTIMGUI_LIB}")
++else()
++    message("Using bundled qtimgui library")
++    set(QTIMGUI_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/3rdparty/qtimgui)
++    set(QTIMGUI_SOURCES
++        ../3rdparty/qtimgui/ImGuiRenderer.cpp
++        ../3rdparty/qtimgui/QtImGui.cpp)
++endif()
++
+ target_include_directories(nextpnr-${target}-gui PRIVATE
+     ${CMAKE_SOURCE_DIR}/frontend
+     ${CMAKE_SOURCE_DIR}/json
+     ${CMAKE_SOURCE_DIR}/3rdparty/QtPropertyBrowser/src
+-    ${CMAKE_SOURCE_DIR}/3rdparty/imgui
+-    ${CMAKE_SOURCE_DIR}/3rdparty/qtimgui
++    ${IMGUI_INCLUDE_DIR}
++    ${QTIMGUI_INCLUDE_DIR}
+ )
+ 
+ target_link_libraries(nextpnr-${target}-gui PUBLIC
+@@ -77,14 +107,17 @@ if (BUILD_PYTHON)
+         ../3rdparty/python-console/ParseMessage.cpp
+         ../3rdparty/python-console/modified/pyredirector.cc
+         ../3rdparty/python-console/modified/pyinterpreter.cc
+-        ../3rdparty/imgui/imgui_widgets.cpp
+-        ../3rdparty/imgui/imgui_draw.cpp
+-        ../3rdparty/imgui/imgui.cpp
+-        ../3rdparty/imgui/imgui_demo.cpp
+-        ../3rdparty/qtimgui/ImGuiRenderer.cpp
+-        ../3rdparty/qtimgui/QtImGui.cpp
++        ${IMGUI_SOURCES}
++        ${QTIMGUI_SOURCES}
+     )
+ 
++    if (IMGUI_LIB)
++        target_link_libraries(nextpnr-${target}-gui PRIVATE ${IMGUI_LIB})
++    endif()
++    if (QTIMGUI_LIB)
++        target_link_libraries(nextpnr-${target}-gui PRIVATE ${QTIMGUI_LIB})
++    endif()
++
+     target_include_directories(nextpnr-${target}-gui PRIVATE
+         ../3rdparty/python-console
+         ../3rdparty/python-console/modified