Improve s390x CPU support (#25056)

TODO list, copied from the documentation:

- [x] compiler/platform.nim Add os/cpu properties.
- [x] lib/system.nim Add os/cpu to the documentation for system.hostOS
and system.hostCPU.
- [x] ~~compiler/options.nim Add special os/cpu property checks in
isDefined.~~ seems unnecessary; isn't dont for most CPUs
- [x] compiler/installer.ini Add os/cpu to Project.Platforms field.
- [x] lib/system/platforms.nim Add os/cpu.
- [x] ~~std/private/osseps.nim Add os specializations.~~
- [x] ~~lib/pure/distros.nim Add os, package handler.~~
- [x] ~~tools/niminst/makefile.nimf Add os/cpu compiler/linker flags.~~
already done in https://github.com/nim-lang/Nim/pull/20943
- [x] tools/niminst/buildsh.nimf Add os/cpu compiler/linker flags.

For csource:

- [x] have compiler/platform.nim updated
- [x] have compiler/installer.ini updated
- [x] have tools/niminst/buildsh.nimf updated
- [x] have tools/niminst/makefile.nimf updated
- [ ] be backported to the Nim version used by the csources
- [ ] the new csources must be pushed
- [ ] the new csources revision must be updated in
config/build_config.txt

Additionally:

- [x] check relation to https://github.com/nim-lang/Nim/pull/20943

Possible future work:

- Porting Nim to s390x-specific operating systems, notably z/OS

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

compiler/installer.ini

@@ -6,7 +6,7 @@ Name: "Nim"
 Version: "$version"
 Platforms: """
   windows: i386;amd64
-  linux: i386;hppa;ia64;alpha;amd64;powerpc64;arm;sparc;sparc64;m68k;mips;mipsel;mips64;mips64el;powerpc;powerpc64el;arm64;riscv32;riscv64;loongarch64
+  linux: i386;hppa;ia64;alpha;amd64;powerpc64;arm;sparc;sparc64;s390x;m68k;mips;mipsel;mips64;mips64el;powerpc;powerpc64el;arm64;riscv32;riscv64;loongarch64
   macosx: i386;amd64;powerpc64;arm64
   solaris: i386;amd64;sparc;sparc64
   freebsd: i386;amd64;powerpc64;arm;arm64;riscv64;sparc64;mips;mipsel;mips64;mips64el;powerpc;powerpc64el

compiler/platform.nim

@@ -210,8 +210,8 @@ type
     cpuNone, cpuI386, cpuM68k, cpuAlpha, cpuPowerpc, cpuPowerpc64,
     cpuPowerpc64el, cpuSparc, cpuVm, cpuHppa, cpuIa64, cpuAmd64, cpuMips,
     cpuMipsel, cpuArm, cpuArm64, cpuJS, cpuNimVM, cpuAVR, cpuMSP430,
-    cpuSparc64, cpuMips64, cpuMips64el, cpuRiscV32, cpuRiscV64, cpuEsp, cpuWasm32,
-    cpuE2k, cpuLoongArch64
+    cpuSparc64, cpuS390x, cpuMips64, cpuMips64el, cpuRiscV32, cpuRiscV64,
+    cpuEsp, cpuWasm32, cpuE2k, cpuLoongArch64
 
 type
   TInfoCPU* = tuple[name: string, intSize: int, endian: Endianness,
@@ -241,6 +241,7 @@ const
     (name: "avr", intSize: 16, endian: littleEndian, floatSize: 32, bit: 16),
     (name: "msp430", intSize: 16, endian: littleEndian, floatSize: 32, bit: 16),
     (name: "sparc64", intSize: 64, endian: bigEndian, floatSize: 64, bit: 64),
+    (name: "s390x", intSize: 64, endian: bigEndian, floatSize: 64, bit: 64),
     (name: "mips64", intSize: 64, endian: bigEndian, floatSize: 64, bit: 64),
     (name: "mips64el", intSize: 64, endian: littleEndian, floatSize: 64, bit: 64),
     (name: "riscv32", intSize: 32, endian: littleEndian, floatSize: 64, bit: 32),

lib/system.nim

@@ -1069,7 +1069,8 @@ const
     ## Possible values:
     ## `"i386"`, `"alpha"`, `"powerpc"`, `"powerpc64"`, `"powerpc64el"`,
     ## `"sparc"`, `"amd64"`, `"mips"`, `"mipsel"`, `"arm"`, `"arm64"`,
-    ## `"mips64"`, `"mips64el"`, `"riscv32"`, `"riscv64"`, `"loongarch64"`.
+    ## `"mips64"`, `"mips64el"`, `"riscv32"`, `"riscv64"`, `"loongarch64"`,
+    ## `"s390x"`.
 
   seqShallowFlag = low(int)
   strlitFlag = 1 shl (sizeof(int)*8 - 2) # later versions of the codegen \

tools/nim.zsh-completion

@@ -78,7 +78,7 @@ _nim() {
     '--opt\:-[optimization mode]:x:(none speed size)'
     '--debugger\:native[use native debugger (gdb)]'
     '--app\:-[generate this type of app (lib=dynamic)]:x:(console gui lib staticlib)'
-    '--cpu\:-[target architecture]:x:(alpha amd64 arm arm64 avr e2k esp hppa i386 ia64 js loongarch64 m68k mips mipsel mips64 mips64el msp430 nimvm powerpc powerpc64 powerpc64el riscv32 riscv64 sparc sparc64 vm wasm32)'
+    '--cpu\:-[target architecture]:x:(alpha amd64 arm arm64 avr e2k esp hppa i386 ia64 js loongarch64 m68k mips mipsel mips64 mips64el msp430 nimvm powerpc powerpc64 powerpc64el riscv32 riscv64 sparc sparc64 s390x vm wasm32)'
     '--gc\:-[memory management algorithm to use (default\: refc)]:x:(refc arc orc markAndSweep boehm go regions none)'
     '--os\:-[operating system to compile for]:x:(AIX Amiga Android Any Atari DOS DragonFly FreeBSD FreeRTOS Genode Haiku iOS Irix JS Linux MacOS MacOSX MorphOS NetBSD Netware NimVM NintendoSwitch OS2 OpenBSD PalmOS Standalone QNX SkyOS Solaris VxWorks Windows)'
     '--panics\:-[turn panics into process termination (default\: off)]:x:(off on)'

tools/niminst/buildsh.nimf

@@ -183,6 +183,8 @@ case $ucpu in
       fi
     fi
     ;;
+  *s390x* )
+    mycpu="s390x" ;;
   *ppc64le* )
     mycpu="powerpc64el" ;;
   *ppc64* )