patch 9.1.0622: MS-Windows: mingw-build can be optimized

Problem:  MS-Windows: mingw-build can be optimized
Solution: use --gc-sections to reduce the size of the executable
          (Ken Takata)

Use the --gc-sections linker option and the -ffunction-sections compiler
option to reduce the size of the executable files.  To make these work,
the -fno-asynchronous-unwind-tables compiler option is also needed.

This is enabled by default and can be disabled by `USE_GC_SECTIONS=no`.

Note: A similar feature has been already used in MSVC. (The /OPT linker
option.)

related: #15350

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/Make_cyg_ming.mak

@@ -130,7 +130,6 @@ ifndef STATIC_STDCPLUS
 STATIC_STDCPLUS=no
 endif
 
-
 # Link against the shared version of libwinpthread by default.  Set
 # STATIC_WINPTHREAD to "yes" to link against static version instead.
 ifndef STATIC_WINPTHREAD
@@ -140,6 +139,12 @@ endif
 # This is used when STATIC_STDCPLUS=yes.
 HAS_GCC_EH=yes
 
+# Reduce the size of the executables by using the --gc-sections linker
+# option.  Set USE_GC_SECTIONS to "no" if you see any issues with this.
+ifndef USE_GC_SECTIONS
+USE_GC_SECTIONS=yes
+endif
+
 # If the user doesn't want gettext, undefine it.
 ifeq (no, $(GETTEXT))
 GETTEXT=
@@ -1093,6 +1098,16 @@ LIB += -lgcc_eh
 LIB += -Wl,-Bstatic -lwinpthread -Wl,-Bdynamic
 endif
 
+# To reduce the file size
+ifeq (yes, $(USE_GC_SECTIONS))
+CFLAGS += -ffunction-sections -fno-asynchronous-unwind-tables
+CXXFLAGS += -fasynchronous-unwind-tables
+LFLAGS += -Wl,--gc-sections
+ ifeq (yes, $(VIMDLL))
+EXELFLAGS += -Wl,--gc-sections
+ endif
+endif
+
 ifeq (yes, $(MAP))
 LFLAGS += -Wl,-Map=$(TARGET).map
 endif

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    622,
 /**/
     621,
 /**/