Support NetBSD/aarch64 (#23616)

I could trivially port Nim to NetBSD/aarch64 because it already
supported NetBSD and aarch64. I only needed to generate `c_code` for
this combination.

(cherry picked from commit 0ba932132e)

compiler/installer.ini

@@ -10,7 +10,7 @@ Platforms: """
   macosx: i386;amd64;powerpc64;arm64
   solaris: i386;amd64;sparc;sparc64
   freebsd: i386;amd64;powerpc64;arm;arm64;riscv64;sparc64;mips;mipsel;mips64;mips64el;powerpc;powerpc64el
-  netbsd: i386;amd64
+  netbsd: i386;amd64;arm64
   openbsd: i386;amd64;arm;arm64
   dragonfly: i386;amd64
   crossos: amd64

lib/pure/distros.nim

@@ -128,6 +128,7 @@ type
 
     BSD
     FreeBSD
+    NetBSD
     OpenBSD
     DragonFlyBSD
 
@@ -169,7 +170,7 @@ proc detectOsImpl(d: Distribution): bool =
   else:
     when defined(bsd):
       case d
-      of Distribution.FreeBSD, Distribution.OpenBSD:
+      of Distribution.FreeBSD, Distribution.NetBSD, Distribution.OpenBSD:
         result = $d in uname()
       else:
         result = false
@@ -252,7 +253,7 @@ proc foreignDepInstallCmd*(foreignPackageName: string): (string, bool) =
       result = ("nix-env -i " & p, false)
     elif detectOs(Solaris) or detectOs(FreeBSD):
       result = ("pkg install " & p, true)
-    elif detectOs(OpenBSD):
+    elif detectOs(NetBSD) or detectOs(OpenBSD):
       result = ("pkg_add " & p, true)
     elif detectOs(PCLinuxOS):
       result = ("rpm -ivh " & p, true)

tools/niminst/buildsh.nimf

@@ -122,6 +122,7 @@ case $uos in
   *netbsd* )
     myos="netbsd"
     LINK_FLAGS="$LINK_FLAGS -lm"
+    ucpu=`uname -p`
     ;;
   *darwin* )
     myos="macosx"

tools/niminst/makefile.nimf

@@ -45,6 +45,7 @@ endif
 ifeq ($(uos),netbsd)
   myos = netbsd
   LDFLAGS += -lm
+  ucpu = $(shell sh -c 'uname -p')
 endif
 ifeq ($(uos),darwin)
   myos = macosx