Support cross-compile install of B2.

Because we use the bootstrap exe for the install it was not possible to cross-compile install B2. This change dynamically chooses which b2.exe to install based on target-os and host-os. When in a cross-compile context, i.e. host-os != target-os, the b2 installed is built from source (and using target-os) instead of using the bootstrap exe.

fixes #358

Jamroot.jam

@@ -1,4 +1,4 @@
-# Copyright 2019 Rene Rivera
+# Copyright 2019-2024 Rene Rivera
 # Copyright 2017 Steven Watanabe
 # Copyright 2016 Vladimir Prus
 # Copyright 2017 Edward Diener
@@ -13,7 +13,6 @@ import errors ;
 import feature ;
 import indirect ;
 import os ;
-# import package ;
 import path ;
 import set ;
 import stage : add-install-dir ;
@@ -130,7 +129,7 @@ obj jamgram.obj
 explicit jamgram.obj ;
 
 local b2_src =
-    [ glob src/engine/*.cpp src/engine/modules/*.cpp :
+    [ glob src/engine/*.cpp :
         src/engine/*nt.cpp src/engine/*unix.cpp src/engine/*vms.cpp
         src/engine/yyacc.cpp src/engine/mkjambase.cpp
         src/engine/check_*.cpp
@@ -180,15 +179,25 @@ add-install-dir b2bindir-portable : : b2prefix-portable ;
 add-install-dir b2coredir-portable : .b2 : b2prefix-portable ;
 add-install-dir b2examplesdir-portable : .b2/examples : b2prefix-portable ;
 
-local ext = "" ;
-if [ os.on-windows ] || [ os.on-vms ]
+rule b2-exe ( props * )
 {
-    ext = ".exe" ;
+    local target-os = [ feature.get-values <target-os> : $(props) ] ;
+    local host-os = [ feature.get-values <host-os> : $(props) ] ;
+    if $(target-os) != $(host-os)
+    {
+        return <source>b2 ;
+    }
+    else if $(target-os) in windows vms
+    {
+        return <source>src/engine/b2.exe ;
+    }
+    return <source>src/engine/b2 ;
 }
 
 install b2-engine
-    :   $(SELF)/src/engine/b2$(ext)
-    :   <b2-install-layout>standard:<location>(b2bindir-standard)
+    :
+    :   <conditional>@b2-exe
+        <b2-install-layout>standard:<location>(b2bindir-standard)
         <b2-install-layout>portable:<location>(b2bindir-portable)
     ;
 explicit b2-engine ;

doc/src/history.adoc

@@ -9,6 +9,8 @@
 * Fix `import-search` failing to find imports on Windows bacause of incorrect
   native vs. non-native path handling.
   -- _René Ferdinand Rivera Morell_
+* Support cross-compile install of B2, using `target-os=xyz`.
+  -- _René Ferdinand Rivera Morell_
 
 == Version 5.0.0