boehmgc: Add patch for RISC-V support.

pkgs/development/libraries/boehm-gc/default.nix

@@ -27,7 +27,9 @@ stdenv.mkDerivation rec {
   patches = [ (fetchpatch {
     url = "https://raw.githubusercontent.com/gentoo/musl/85b6a600996bdd71162b357e9ba93d8559342432/dev-libs/boehm-gc/files/boehm-gc-7.6.0-sys_select.patch";
     sha256 = "1gydwlklvci30f5dpp5ccw2p2qpph5y41r55wx9idamjlq66fbb3";
-  }) ];
+  }) ] ++
+    # https://github.com/ivmai/bdwgc/pull/208
+    lib.optional hostPlatform.isRiscV ./riscv.patch;
 
   configureFlags =
     [ "--enable-cplusplus" ]

pkgs/development/libraries/boehm-gc/riscv.patch

@@ -0,0 +1,53 @@
+diff --git a/include/private/gcconfig.h b/include/private/gcconfig.h
+index a8e55dd2..439cc88d 100644
+--- a/include/private/gcconfig.h
++++ b/include/private/gcconfig.h
+@@ -650,6 +650,15 @@
+ #   endif
+ #   define mach_type_known
+ # endif
++# if defined(__riscv) && defined(LINUX)
++#   if __riscv_xlen == 32
++#     define RISCV32
++#     define mach_type_known
++#   elif __riscv_xlen == 64
++#     define RISCV64
++#     define mach_type_known
++#   endif
++# endif
+ 
+ # if defined(SN_TARGET_PSP2)
+ #   define mach_type_known
+@@ -2970,6 +2979,32 @@
+ #   endif
+ # endif
+ 
++# ifdef RISCV32
++#   define CPP_WORDSZ 32
++#   define MACH_TYPE "RISC-V 32"
++#   define ALIGNMENT 4
++#   ifdef LINUX
++#     define OS_TYPE "LINUX"
++      extern int __data_start[];
++#     define DATASTART ((ptr_t)__data_start)
++#     define LINUX_STACKBOTTOM
++#     define DYNAMIC_LOADING
++#   endif
++# endif
++
++# ifdef RISCV64
++#   define CPP_WORDSZ 64
++#   define MACH_TYPE "RISC-V 64"
++#   define ALIGNMENT 8
++#   ifdef LINUX
++#     define OS_TYPE "LINUX"
++      extern int __data_start[];
++#     define DATASTART ((ptr_t)__data_start)
++#     define LINUX_STACKBOTTOM
++#     define DYNAMIC_LOADING
++#   endif
++# endif
++
+ #if defined(__GLIBC__) && !defined(DONT_USE_LIBC_PRIVATES)
+   /* Use glibc's stack-end marker. */
+ # define USE_LIBC_PRIVATES