Issue #29080: Removes hard dependency on hg.exe from PC/build.bat

Misc/NEWS

@@ -597,6 +597,8 @@ Documentation
 Build
 -----
 
+- Issue #29080: Removes hard dependency on hg.exe from PC/build.bat
+
 - Issue #23903: Added missed names to PC/python3.def.
 
 - Issue #28762: lockf() is available on Android API level 24, but the F_LOCK

PCbuild/build.bat

@@ -106,7 +106,8 @@ if "%platf%"=="x64" (
 )
 
 if not exist "%HG%" where hg > "%TEMP%\hg.loc" 2> nul && set /P HG= < "%TEMP%\hg.loc" & del "%TEMP%\hg.loc"
-if not exist "%HG%" echo Cannot find Mercurial on PATH && exit /B 1
+if exist "%HG%" set HGProperty=/p:HG="%HG%"
+if not exist "%HG%" echo Cannot find Mercurial on PATH & set HGProperty=
 
 rem Setup the environment
 call "%dir%env.bat" %vs_platf% >nul
@@ -144,8 +145,7 @@ msbuild "%dir%pcbuild.proj" /t:%target% %parallel% %verbose%^
  /p:Configuration=%conf% /p:Platform=%platf%^
  /p:IncludeExternals=%IncludeExternals%^
  /p:IncludeSSL=%IncludeSSL% /p:IncludeTkinter=%IncludeTkinter%^
- /p:UseTestMarker=%UseTestMarker%^
- /p:HG="%HG%"^
+ /p:UseTestMarker=%UseTestMarker% %HGProperty%^
  %1 %2 %3 %4 %5 %6 %7 %8 %9
 
 @echo off