Cygwin should have EXE=.exe (#2266)

Changes

@@ -578,6 +578,10 @@ OCaml 4.08.0
   then encoding is UTF-8 with code page fallback.
   (Nicolás Ojeda Bär, review by Sébastien Hinderer and David Allsopp)
 
+- GPR#2266: ensure Cygwin ports configure with `EXE=.exe`, or the compiler is
+  unable to find the camlheader files (subtle regression of GPR#2139/2041)
+  (David Allsopp, report and review by Sébastien Hinderer)
+
 ### Internal/compiler-libs changes:
 
 - MPR#7918, GPR#1703, GPR#1944, GPR#2213, GPR#2257: Add the module

configure

@@ -12316,7 +12316,6 @@ esac
 case $host in #(
   *-*-mingw32|*-pc-windows) :
     unix_or_win32="win32"
-    exeext=".exe"
     unixlib="win32unix"
     graphlib="win32graph"
     cc_profile='' ;; #(
@@ -12326,6 +12325,12 @@ case $host in #(
   graphlib="graph"
   cc_profile='-pg' ;;
 esac
+case $host in #(
+  *-*-cygwin*|*-*-mingw32|*-pc-windows) :
+    exeext=".exe" ;; #(
+  *) :
+    exeext='' ;;
+esac
 
 otherlibraries="dynlink"
 if test x"$enable_unix_lib" != "xno"; then :

configure.ac

@@ -414,7 +414,6 @@ AS_CASE([$host],
 AS_CASE([$host],
   [*-*-mingw32|*-pc-windows],
     [unix_or_win32="win32"
-    exeext=".exe"
     unixlib="win32unix"
     graphlib="win32graph"
     cc_profile=''],
@@ -422,6 +421,10 @@ AS_CASE([$host],
   unixlib="unix"
   graphlib="graph"
   cc_profile='-pg'])
+AS_CASE([$host],
+  [*-*-cygwin*|*-*-mingw32|*-pc-windows],
+    [exeext=".exe"],
+  [exeext=''])
 
 otherlibraries="dynlink"
 AS_IF([test x"$enable_unix_lib" != "xno"],