Changes to make aclocal.m4 aware of the hadrian '_build' directory

ghc-aclocal.m4.patch

diff --git a/aclocal.m4 b/aclocal.m4
index dcc3448..05c4cc6 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -945,7 +945,8 @@ else
 fi;
 changequote([, ])dnl
 ])
-if test ! -f compiler/parser/Parser.hs || test ! -f compiler/cmm/CmmParse.hs
+if   test ! \( -f compiler/parser/Parser.hs -o -f _build/stage1/compiler/Parser.hs \) \
+  || test ! \( -f compiler/cmm/CmmParse.hs  -o -f _build/stage1/compiler/CmmParse.hs \)
 then
     FP_COMPARE_VERSIONS([$fptools_cv_happy_version],[-lt],[1.19.4],
       [AC_MSG_ERROR([Happy version 1.19.4 or later is required to compile GHC.])])[]
@@ -975,7 +976,8 @@ changequote([, ])dnl
 ])
 FP_COMPARE_VERSIONS([$fptools_cv_alex_version],[-ge],[3.0],
   [Alex3=YES],[Alex3=NO])
-if test ! -f compiler/cmm/CmmLex.hs || test ! -f compiler/parser/Lexer.hs
+if   test ! \( -f compiler/cmm/CmmLex.hs   -o -f _build/stage1/compiler/CmmLex.hs \) \
+  || test ! \( -f compiler/parser/Lexer.hs -o -f _build/stage1/compiler/Lexer.hs \)
 then
     FP_COMPARE_VERSIONS([$fptools_cv_alex_version],[-lt],[3.1.0],
       [AC_MSG_ERROR([Alex version 3.1.0 or later is required to compile GHC.])])[]