Proper Makefile for cross compiling 64 or 32 bit PGO + LTO + static Windows binaries under Linux.

No functional change

Resolves #511

src/Makefile

@@ -159,7 +159,25 @@ endif
 
 ifeq ($(COMP),mingw)
 	comp=mingw
-	CXX=g++
+
+	ifeq ($(UNAME),Linux)
+		ifeq ($(bits),64)
+			ifeq ($(shell which x86_64-w64-mingw32-c++-posix),)
+				CXX=x86_64-w64-mingw32-c++
+			else
+				CXX=x86_64-w64-mingw32-c++-posix
+			endif
+		else
+			ifeq ($(shell which i686-w64-mingw32-c++-posix),)
+				CXX=i686-w64-mingw32-c++
+			else
+				CXX=i686-w64-mingw32-c++-posix
+			endif
+		endif
+	else
+		CXX=g++
+	endif
+
 	CXXFLAGS += -Wextra -Wshadow
 	LDFLAGS += -static
 endif
@@ -307,7 +325,7 @@ ifeq ($(pext),yes)
 	endif
 endif
 
-### 3.11 Link Time Optimization, it works since gcc 4.5 but not on mingw.
+### 3.11 Link Time Optimization, it works since gcc 4.5 but not on mingw under Windows.
 ### This is a mix of compile and link time options because the lto link phase
 ### needs access to the optimization flags.
 ifeq ($(comp),gcc)
@@ -319,6 +337,17 @@ ifeq ($(comp),gcc)
 	endif
 endif
 
+ifeq ($(comp),mingw)
+	ifeq ($(UNAME),Linux)
+	ifeq ($(optimize),yes)
+	ifeq ($(debug),no)
+		CXXFLAGS += -flto
+		LDFLAGS += $(CXXFLAGS)
+	endif
+	endif
+	endif
+endif
+
 ### 3.12 Android 5 can only run position independent executables. Note that this
 ### breaks Android 4.0 and earlier.
 ifeq ($(arch),armv7)