gnu: grfcodec: Fix build with GCC 10.

* gnu/packages/patches/grfcodec-gcc-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/game-development.scm (grfcodec)[source](patches): New field.
[arguments]: Remove trailing #t.

gnu/local.mk

@@ -1199,6 +1199,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/gpsbabel-fix-i686-test.patch		\
   %D%/packages/patches/grantlee-merge-theme-dirs.patch		\
   %D%/packages/patches/grep-timing-sensitive-test.patch		\
+  %D%/packages/patches/grfcodec-gcc-compat.patch		\
   %D%/packages/patches/grocsvs-dont-use-admiral.patch		\
   %D%/packages/patches/gromacs-tinyxml2.patch			\
   %D%/packages/patches/groovy-add-exceptionutilsgenerator.patch	\

gnu/packages/game-development.scm

@@ -213,6 +213,7 @@ (define-public grfcodec
        (uri (string-append "https://binaries.openttd.org/extra/"
                            name "/" version "/" name "-" version
                            "-source.tar.xz"))
+       (patches (search-patches "grfcodec-gcc-compat.patch"))
        (sha256
         (base32 "08admgnpqcsifpicbm56apgv360fxapqpbbsp10qyk8i22w1ivsk"))))
     (build-system gnu-build-system)
@@ -238,8 +239,7 @@ (define-public grfcodec
                              "readme" "readme.rpn"))
                  (for-each (lambda (file)
                              (install-file file man))
-                           (find-files "." "\\.1"))))
+                           (find-files "." "\\.1")))))))))
-             #t)))))
     (inputs
      (list boost libpng zlib))
     (synopsis "GRF development tools")

gnu/packages/patches/grfcodec-gcc-compat.patch

@@ -0,0 +1,31 @@
+Fix type comparison issue that is a hard error in GCC 10.
+
+Taken from upstream:
+
+  https://github.com/OpenTTD/grfcodec/commit/bb692b2c723c5e87cc8f89f445928e97594d5b8f
+
+diff --git a/src/command.cpp b/src/command.cpp
+index 9aa0e14..1f32cf1 100644
+--- a/src/command.cpp
++++ b/src/command.cpp
+@@ -300,8 +300,9 @@ bool parse_comment(const string&line){
+ 		break;
+ 	case BEAUTIFY:{
+ 		commandstream>>command_part;
+-		uint val=find_command(command_part,beaut),togglebit;
+-		if(val!=(uint)-1&&val!=OFF)_commandState.beautifier=true;
++		int val=find_command(command_part,beaut);
++		uint togglebit;
++		if(val!=-1&&val!=OFF)_commandState.beautifier=true;
+ 		switch(val){
+ 		case -1:
+ 			IssueMessage(0,COMMAND_INVALID_ARG,gen[BEAUTIFY].name);
+@@ -372,7 +373,7 @@ bool parse_comment(const string&line){
+ dotoggle:
+ 			commandstream>>command_part;
+ 			val=find_command(command_part,beaut);
+-			if(!commandstream||val==(uint)-1){
++			if(!commandstream||val==-1){
+ 				IssueMessage(0,COMMAND_INVALID_ARG,gen[BEAUTIFY].name);
+ 				return true;
+ 			}