libXNVCtrl: build shared library

The libXNVCtrl library is used by several programs in nixpkgs to get
Nvidia GPU stats, and they all load the library dynamically, but the
libXNVCtrl package only builds a static library.  There is no build flag
to enable this, so we have to patch the Makefile to produce a shared
library.

Based on a patch by @negativo17 for Fedora.
https://github.com/negativo17/nvidia-settings/blob/master/nvidia-settings-libXNVCtrl.patch

pkgs/os-specific/linux/nvidia-x11/libxnvctrl-build-shared-3xx.patch

@@ -0,0 +1,24 @@
+--- a/src/libXNVCtrl/Makefile
++++ b/src/libXNVCtrl/Makefile
+@@ -33,6 +33,8 @@
+ 
+ LIBXNVCTRL = libXNVCtrl.a
+ 
++LIBXNVCTRL_SHARED = $(OUTPUTDIR)/libXNVCtrl.so
++
+ LIBXNVCTRL_PROGRAM_NAME = "libXNVCtrl"
+ 
+ LIBXNVCTRL_VERSION := $(NVIDIA_VERSION)
+@@ -62,6 +64,12 @@
+ $(LIBXNVCTRL) : $(OBJS)
+ 	$(AR) ru $@ $(OBJS)
+ 
++$(LIBXNVCTRL_SHARED): $(LIBXNVCTRL_OBJ)
++	$(RM) $@ $@.*
++	$(CC) -shared -Wl,-soname=$(@F).0 -o $@.0.0.0 $(LDFLAGS) $^ -lXext -lX11
++	ln -s $(@F).0.0.0 $@.0
++	ln -s $(@F).0 $@
++
+ # define the rule to build each object file
+ $(foreach src,$(SRC),$(eval $(call DEFINE_OBJECT_RULE,TARGET,$(src))))
+ 

pkgs/os-specific/linux/nvidia-x11/libxnvctrl-build-shared.patch

@@ -0,0 +1,21 @@
+--- a/src/libXNVCtrl/xnvctrl.mk
++++ b/src/libXNVCtrl/xnvctrl.mk
+@@ -39,6 +39,8 @@
+ 
+ LIBXNVCTRL = $(OUTPUTDIR)/libXNVCtrl.a
+ 
++LIBXNVCTRL_SHARED = $(OUTPUTDIR)/libXNVCtrl.so
++
+ LIBXNVCTRL_SRC = $(XNVCTRL_DIR)/NVCtrl.c
+ 
+ LIBXNVCTRL_OBJ = $(call BUILD_OBJECT_LIST,$(LIBXNVCTRL_SRC))
+@@ -47,3 +49,9 @@
+ 
+ $(LIBXNVCTRL) : $(LIBXNVCTRL_OBJ)
+ 	$(call quiet_cmd,AR) ru $@ $(LIBXNVCTRL_OBJ)
++
++$(LIBXNVCTRL_SHARED): $(LIBXNVCTRL_OBJ)
++	$(RM) $@ $@.*
++	$(CC) -shared -Wl,-soname=$(@F).0 -o $@.0.0.0 $(LDFLAGS) $^ -lXext -lX11
++	ln -s $(@F).0.0.0 $@.0
++	ln -s $(@F).0 $@

pkgs/os-specific/linux/nvidia-x11/settings.nix

@@ -43,6 +43,14 @@ let
 
     makeFlags = [
       "OUTPUTDIR=." # src/libXNVCtrl
+      "libXNVCtrl.a"
+      "libXNVCtrl.so"
+    ];
+
+    patches = [
+      # Patch the Makefile to also produce a shared library.
+      (if lib.versionOlder nvidia_x11.settingsVersion "400" then ./libxnvctrl-build-shared-3xx.patch
+      else ./libxnvctrl-build-shared.patch)
     ];
 
     installPhase = ''
@@ -52,6 +60,7 @@ let
       cp libXNVCtrl.a $out/lib
       cp NVCtrl.h     $out/include/NVCtrl
       cp NVCtrlLib.h  $out/include/NVCtrl
+      cp -P libXNVCtrl.so* $out/lib
     '';
   };