Fix host architecture detection for canadian cross builds

If the host architecture is different from -platform (canadian cross
build with -external-hostbindir) then we cannot use QMAKE_HOST.os to
deduce the executable extension for that platform, because this value
comes from the qmake binary that was pointed to by
-external-hostbindir.

Move the target name deduction mechanism to the actual configure test
.pro files to make sure the right scopes are available, and write the
deduced target name to a text file. That text file is read by
qtConfTest_architecture to get the right binary to analyze.

Fixes: QTBUG-77286
Change-Id: I68b844dd51dbfda6432a4b0dca6331899c82255f
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

config.tests/arch/arch.pro

@@ -1 +1,2 @@
 SOURCES = arch.cpp
+include(write_info.pri)

config.tests/arch/arch_host.pro

@@ -1,2 +1,3 @@
 option(host_build)
 SOURCES = arch.cpp
+include(write_info.pri)

config.tests/arch/write_info.pri

@@ -0,0 +1,14 @@
+targetinfofile = $$basename(_PRO_FILE_)
+targetinfofile ~= s/pro$/target.txt/
+
+win32 {
+    ext = .exe
+} else:android {
+    file_prefix = lib
+    ext = .so
+} else:wasm {
+    ext = .wasm
+}
+
+content = $${file_prefix}$${TARGET}$${ext}
+write_file($$OUT_PWD/$$targetinfofile, content)

configure.pri

@@ -266,28 +266,10 @@ defineTest(qtConfTest_architecture) {
     !qtConfTest_compile($${1}): \
         error("Could not determine $$eval($${1}.label). See config.log for details.")
 
-    host = $$eval($${1}.host)
-    isEmpty(host): host = false
-    file_prefix =
-    ext =
-    $$host {
-        equals(QMAKE_HOST.os, Windows): \
-            ext = .exe
-    } else {
-        win32 {
-            ext = .exe
-        } else:android {
-            file_prefix = lib
-            ext = .so
-        } else:wasm {
-            ext = .wasm
-        }
-    }
-
     test = $$eval($${1}.test)
     output = $$eval($${1}.output)
     test_out_dir = $$OUT_PWD/$$basename(QMAKE_CONFIG_TESTS_DIR)/$$test
-    test_out_file = $$test_out_dir/$$file_prefix$$output$$ext
+    test_out_file = $$test_out_dir/$$cat($$test_out_dir/$${output}.target.txt)
     exists($$test_out_file): \
         content = $$cat($$test_out_file, blob)
     else: \