The -o flag should not strip extensions except for .exe

Current the -o flag will strip any "extension" on the provided filename,
which is fairly problimatic on Linux and Mac OS since those executes do
not have other extensions and names like "foobar.v1" will get the ".v1"
stripped off. This can happen on Windows as well if you leave off the
.exe (QB64-PE will add it for you, but also strip off the existing
extension).

QB64-PE stripping off the ".exe" when provided that on Linux and Mac OS
might actually be useful behavior people are relying on (so that they
don't need to provide different names when compiling on Linux/Mac OS) so
we are preserving that and still removing the extension if it is exactly
"EXE", otherwise we now leave it in place.

Fixes: #297

source/qb64pe.bas

@@ -12322,7 +12322,12 @@ IF idemode = 0 AND No_C_Compile_Mode = 0 THEN
             'resolve relative path for output file
             path.out$ = getfilepath$(outputfile_cmd$)
             f$ = MID$(outputfile_cmd$, LEN(path.out$) + 1)
-            file$ = RemoveFileExtension$(f$)
+
+            If UCASE$(GetFileExtension$(f$)) = "EXE" Then
+                file$ = RemoveFileExtension$(f$)
+            Else
+                file$ = f$
+            End If
         END IF
 
         IF LEN(path.out$) OR OutputIsRelativeToStartDir THEN

source/utilities/file.bas

@@ -71,6 +71,20 @@ FUNCTION RemoveFileExtension$ (f$)
     RemoveFileExtension$ = f$
 END FUNCTION
 
+'
+' Returns the extension on the end of a file name
+'
+' Returns "" if there is no extension
+'
+FUNCTION GetFileExtension$ (f$)
+    FOR i = LEN(f$) TO 1 STEP -1
+        a = ASC(f$, i)
+        IF a = 47 OR a = 92 THEN EXIT FOR
+        IF a = 46 THEN GetFileExtension$ = MID$(f$, i + 1): EXIT FUNCTION
+    NEXT
+    GetFileExtension$ = ""
+END FUNCTION
+
 '
 ' Fixes the provided filename and path to use the correct path separator
 '

tests/compile_tests/filename/filename.extra.extension.bas

@@ -0,0 +1,2 @@
+$Console:Only
+System

tests/compile_tests/qb64pe/file.bas

@@ -0,0 +1,41 @@
+DEFLNG A-Z
+$Console:Only
+
+Type TestCase
+    file As String
+    expectedExtension As String
+End Type
+
+Dim tests(5) As TestCase
+
+tests(1).file = "foobar.exe"
+tests(1).expectedExtension = "exe"
+
+tests(2).file = "foobar.EXE"
+tests(2).expectedExtension = "EXE"
+
+tests(3).file = "foobar."
+tests(3).expectedExtension = ""
+
+tests(4).file = "foobar"
+tests(4).expectedExtension = ""
+
+tests(5).file = "foobar.tar.gz"
+tests(5).expectedExtension = "gz"
+
+For i = 1 To UBOUND(tests)
+    result$ = GetFileExtension$(tests(i).file)
+
+    Print "Test"; i; ", Filename: "; tests(i).file
+    Print "    Expected: "; tests(i).expectedExtension; ", Actual: "; result$
+
+    If result$ = tests(i).expectedExtension Then
+        Print "      PASS!"
+    Else
+        Print "      FAIL!"
+    End If
+Next
+
+System
+
+'$include:'../../../source/utilities/file.bas'

tests/compile_tests/qb64pe/file.output

@@ -0,0 +1,15 @@
+Test 1 , Filename: foobar.exe
+    Expected: exe, Actual: exe
+      PASS!
+Test 2 , Filename: foobar.EXE
+    Expected: EXE, Actual: EXE
+      PASS!
+Test 3 , Filename: foobar.
+    Expected: , Actual: 
+      PASS!
+Test 4 , Filename: foobar
+    Expected: , Actual: 
+      PASS!
+Test 5 , Filename: foobar.tar.gz
+    Expected: gz, Actual: gz
+      PASS!