--disable-gil doesn't support --enable-experimental-jit

Author: brandtbucher

PCbuild/build.bat

@@ -123,6 +123,13 @@ if "%do_pgo%" EQU "true" if "%platf%" EQU "x64" (
     )
 )
 
+if "%UseDisableGil%" EQU "true" if "%UseTIER2%" NEQ "" (
+    rem GH-133171: This configuration builds the JIT but never actually uses it,
+    rem which is surprising (and strictly worse than not building it at all):
+    echo.ERROR: --experimental-jit cannot be used with --disable-gil.
+    exit /b 1
+)
+
 if not exist "%GIT%" where git > "%TEMP%\git.loc" 2> nul && set /P GIT= < "%TEMP%\git.loc" & del "%TEMP%\git.loc"
 if exist "%GIT%" set GITProperty=/p:GIT="%GIT%"
 if not exist "%GIT%" echo Cannot find Git on PATH & set GITProperty=

configure

@@ -1837,6 +1837,12 @@ AC_SUBST([REGEN_JIT_COMMAND])
 AC_SUBST([JIT_STENCILS_H])
 AC_MSG_RESULT([$tier2_flags $jit_flags])
 
+if test "$disable_gil" = "yes" -a "$enable_experimental_jit" != "no"; then
+  # GH-133171: This configuration builds the JIT but never actually uses it,
+  # which is surprising (and strictly worse than not building it at all):
+  AC_MSG_ERROR([--enable-experimental-jit cannot be used with --disable-gil.])
+fi
+
 # Enable optimization flags
 AC_SUBST([DEF_MAKE_ALL_RULE])
 AC_SUBST([DEF_MAKE_RULE])