Makefile.win: definitions and objects agree, and imm32 links

Two kinds of drift a direct mingw build tripped over, found while
building the audit lane. DEFINES has carried -DHAVE_OVERLAY since
before the object list moved to Makefile.common, which keys off the
make variables: the define without the variable compiled overlay
callers against overlay objects that were never built, and
screenshots without HAVE_RPNG could not encode - both surfacing as
undefined references at link. The variables are now set where the
other HAVE_ ones are, so definitions and objects agree again.

And win32_common.c pulls imm32 with #pragma comment(lib), which
MSVC honours and GNU ld silently ignores, leaving the IME
composition calls undefined; the library is now on LIBS explicitly.

The audit lane script drops both of its compensations - the
variable overrides and the manual relink that appended imm32 - and
its plain make now compiles and links the audit subject in one
step, which is the fix demonstrating itself.

Verified: a clean cross build linking through the makefile's own
rule, and the PE audit at its standing zero findings.

Makefile.win

@@ -1,6 +1,14 @@
 TARGET = retroarch.exe
 
 HAVE_SCREENSHOTS = 1
+# DEFINES below has carried -DHAVE_OVERLAY since before the object
+# list moved to Makefile.common, which keys off these variables: the
+# define without the variable compiled overlay callers against
+# overlay objects that were never built, and screenshots without
+# rpng could not encode. Set the variables so definitions and
+# objects agree again.
+HAVE_OVERLAY = 1
+HAVE_RPNG = 1
 HAVE_AUDIOMIXER = 1
 HAVE_RWAV = 1
 HAVE_DINPUT = 1
@@ -95,7 +103,10 @@ OBJDIR           := obj-w32
 
 OS               := Win32
 OBJ              :=
-LIBS             := -lm
+# imm32: win32_common.c pulls it with #pragma comment(lib), which
+# MSVC honours and GNU ld silently ignores - link it explicitly or
+# the IME composition calls are undefined under mingw.
+LIBS             := -lm -limm32
 DEFINES			  :=
 DEFINES          += -I. -Ilibretro-common/include -DRARCH_INTERNAL -DHAVE_SCREENSHOTS -DHAVE_OVERLAY
 LDFLAGS          := -L. -static-libgcc

tools/mingw-audit-build.sh

@@ -8,10 +8,8 @@
 # from older mingw-w64 (d3dkmthk.h; the unversioned d3d12 serialize
 # PFN; three D3D interface names mapped to IUnknown - layout is
 # irrelevant, only call edges are read), and imm32 is appended by
-# relinking manually because Makefile.win assigns LIBS with := so no
-# variable reaches the link from outside. HAVE_OVERLAY and HAVE_RPNG
-# are set because Makefile.win's DEFINES already assume them while
-# the object list keys off the make variables.
+# (Makefile.win now links imm32 and sets HAVE_OVERLAY/HAVE_RPNG
+# itself, so this script no longer compensates for either.)
 # Usage: tools/mingw-audit-build.sh   (then:)
 #   python3 tools/thread_read_audit.py --binary retroarch.exe \
 #     --objdump x86_64-w64-mingw32-objdump
@@ -22,8 +20,6 @@ export CFLAGS="-I$STUBS -include $STUBS/d3d12_fixup.h \
 -DID3D12InfoQueue=IUnknown -DD3D12_MAX_TEXTURE_DIMENSION_2_TO_EXP=17"
 MK="make -f Makefile.win HOST_PREFIX=x86_64-w64-mingw32- \
 CXX=x86_64-w64-mingw32-gcc HAVE_D3D11=1 HAVE_D3D12=1 HAVE_FREETYPE=0 \
-HAVE_CG=0 HAVE_XAUDIO=0 HAVE_OVERLAY=1 HAVE_RPNG=1"
-$MK -j"$(nproc)" || true   # everything except the exe rule's link
-$MK -n 2>/dev/null | grep "o retroarch.exe" | head -1 \
-   | sed 's/$/ -limm32/' | sh
+HAVE_CG=0 HAVE_XAUDIO=0"
+$MK -j"$(nproc)"
 ls -la retroarch.exe