v.pref,v.builder: support overriding the C cross compiler by setting `VCROSS_COMPILER_NAME`

cmd/v/help/build-c.txt

@@ -119,7 +119,12 @@ see also `v help build`.
       explicitly supported platforms without source changes.
 
    -m32, -m64
-      Specify whether 32-bit or 64-bit machine code is generated.
+      Whether 32-bit or 64-bit machine code will be generated.
+      NB: if you need to produce 32-bit code, *and* you are cross compiling
+      to another OS, you may need to also set the environment variable
+      VCROSS_COMPILER_NAME, in order to override the default cross compiler,
+      that V will use (`x86_64-w64-mingw32-gcc` for targeting Windows, and
+      `clang` for targeting Linux from other operating systems).
 
    -sanitize
       Pass flags related to sanitization to the C compiler.

vlib/v/builder/cc.v

@@ -39,10 +39,6 @@ You can also seek #help on Discord: https://discord.gg/vlang
 '
 )
 
-const (
-	mingw_cc = 'x86_64-w64-mingw32-gcc'
-)
-
 fn (mut v Builder) find_win_cc() ? {
 	$if !windows {
 		return
@@ -900,7 +896,7 @@ fn (mut c Builder) cc_windows_cross() {
 	all_args << args
 	all_args << '-municode'
 	c.dump_c_options(all_args)
-	mut cmd := '$builder.mingw_cc ' + all_args.join(' ')
+	mut cmd := pref.vcross_compiler_name(pref.cc_to_windows) + ' ' + all_args.join(' ')
 	// cmd := 'clang -o $obj_name -w $include -m32 -c -target x86_64-win32 ${pref.default_module_path}/$c.out_name_c'
 	if c.pref.is_verbose || c.pref.show_cc {
 		println(cmd)

vlib/v/pref/default.v

@@ -138,6 +138,10 @@ pub fn (mut p Preferences) fill_with_defaults() {
 	}
 }
 
+pub const cc_to_windows = 'x86_64-w64-mingw32-gcc'
+
+pub const cc_to_linux = 'clang'
+
 fn (mut p Preferences) find_cc_if_cross_compiling() {
 	if p.os == .windows {
 		$if !windows {
@@ -147,14 +151,14 @@ fn (mut p Preferences) find_cc_if_cross_compiling() {
 			// options).
 			if p.ccompiler != 'msvc' {
 				// Cross compiling to Windows
-				p.ccompiler = 'x86_64-w64-mingw32-gcc'
+				p.ccompiler = vcross_compiler_name(pref.cc_to_windows)
 			}
 		}
 	}
 	if p.os == .linux {
 		$if !linux {
 			// Cross compiling to Linux
-			p.ccompiler = 'clang'
+			p.ccompiler = vcross_compiler_name(pref.cc_to_linux)
 		}
 	}
 }
@@ -210,3 +214,11 @@ pub fn vexe_path() string {
 	os.setenv('VEXE', real_vexe_path, true)
 	return real_vexe_path
 }
+
+pub fn vcross_compiler_name(vccname_default string) string {
+	vccname := os.getenv('VCROSS_COMPILER_NAME')
+	if vccname != '' {
+		return vccname
+	}
+	return vccname_default
+}