Merge #16837: depends: qt: Fix {C{,XX},LD}FLAGS pickup

1b4030e depends: qt: Fix LDFLAGS pickup (Carl Dong)
6eb12ff depends: qt: Fix C{,XX}FLAGS pickup (Carl Dong)

Pull request description:

  Note: ~~Will~~ [Did](bitcoin/bitcoin#16838) open issue about robustness of `sed` calls in `depends`.

ACKs for top commit:
  laanwj:
    ACK 1b4030e

Tree-SHA512: d0bfc8ea32118cd90bb323efab58661f2218a2cb0f150e716cfd5355c7e2a1eba70298a144b159941248170e2894659c376219edac2c79a9d777f6ada5fa6b2f

Author: laanwj

depends/packages/qt.mk

@@ -176,9 +176,9 @@ define $(package)_preprocess_cmds
   patch -p1 -i $($(package)_patch_dir)/no-xlib.patch &&\
   echo "QMAKE_LINK_OBJECT_MAX = 10" >> qtbase/mkspecs/win32-g++/qmake.conf &&\
   echo "QMAKE_LINK_OBJECT_SCRIPT = object_script" >> qtbase/mkspecs/win32-g++/qmake.conf &&\
-  sed -i.old "s|QMAKE_CFLAGS            = |!host_build: QMAKE_CFLAGS            = $($(package)_cflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
-  sed -i.old "s|QMAKE_LFLAGS            = |!host_build: QMAKE_LFLAGS            = $($(package)_ldflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
-  sed -i.old "s|QMAKE_CXXFLAGS          = |!host_build: QMAKE_CXXFLAGS            = $($(package)_cxxflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
+  sed -i.old "s|QMAKE_CFLAGS           += |!host_build: QMAKE_CFLAGS            = $($(package)_cflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
+  sed -i.old "s|QMAKE_CXXFLAGS         += |!host_build: QMAKE_CXXFLAGS            = $($(package)_cxxflags) $($(package)_cppflags) |" qtbase/mkspecs/win32-g++/qmake.conf && \
+  sed -i.old "0,/^QMAKE_LFLAGS_/s|^QMAKE_LFLAGS_|!host_build: QMAKE_LFLAGS            = $($(package)_ldflags)\n&|" qtbase/mkspecs/win32-g++/qmake.conf && \
   sed -i.old "s/LIBRARY_PATH/(CROSS_)?\0/g" qtbase/mkspecs/features/toolchain.prf
 endef