GHA/windows: pass preprocessor flags via `CPPFLAGS`

To avoid potential warning with autotools when using `CFLAGS`. Existing
jobs are not affected.

Also:
- drop a redundant `export`.
- ensure not to overwrite per-job options with UWP ones.

Closes #20857

diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 2e990832fcfe9fb280a46427f47ccb04da278f80..44ac46ad29424d9d54437383f28703ca26180721 100644 (file)
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -258,7 +258,7 @@ jobs:
           - { build: 'cmake'    , sys: 'clang64'   , env: 'clang-x86_64' , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=OFF -DCURL_USE_OPENSSL=ON  -DENABLE_UNICODE=OFF -DUSE_NGTCP2=ON', install: 'mingw-w64-clang-x86_64-openssl mingw-w64-clang-x86_64-nghttp3 mingw-w64-clang-x86_64-ngtcp2 mingw-w64-clang-x86_64-libssh2', type: 'Release', name: 'openssl', chkprefill: '_chkprefill' }
           - { build: 'cmake'    , sys: 'ucrt64'    , env: 'ucrt-x86_64'  , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=OFF -DBUILD_SHARED_LIBS=ON  -DCURL_USE_OPENSSL=ON', install: 'mingw-w64-ucrt-x86_64-openssl mingw-w64-ucrt-x86_64-libssh2', type: 'Release', test: 'uwp', name: 'schannel' }
           # { build: 'autotools', sys: 'ucrt64'    , env: 'ucrt-x86_64'  , tflags: 'skiprun'   , config: '--without-debug --with-schannel --disable-static', install: 'mingw-w64-ucrt-x86_64-libssh2', type: 'Release', test: 'uwp', name: 'schannel' }
-          - { build: 'cmake'    , sys: 'mingw64'   , env: 'x86_64'       , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=ON  -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DCMAKE_VERBOSE_MAKEFILE=ON', install: 'mingw-w64-x86_64-libssh2', type: 'Debug', cflags: '-DCURL_SCHANNEL_DEV_DEBUG', name: 'schannel dev debug', image: 'windows-2025' }
+          - { build: 'cmake'    , sys: 'mingw64'   , env: 'x86_64'       , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=ON  -DBUILD_SHARED_LIBS=ON  -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON -DCMAKE_VERBOSE_MAKEFILE=ON', install: 'mingw-w64-x86_64-libssh2', type: 'Debug', cppflags: '-DCURL_SCHANNEL_DEV_DEBUG', name: 'schannel dev debug', image: 'windows-2025' }
           - { build: 'cmake'    , sys: 'mingw32'   , env: 'i686'         , tflags: 'skiprun'   , config: '-DENABLE_DEBUG=OFF -DBUILD_SHARED_LIBS=ON  -DCURL_USE_SCHANNEL=ON -DENABLE_UNICODE=ON', install: 'mingw-w64-i686-libssh2', type: 'Release', name: 'schannel R' }
       fail-fast: false
     steps:
@@ -301,7 +301,7 @@ jobs:
       - name: 'configure'
         timeout-minutes: 5
         env:
-          CFLAGS: '${{ matrix.cflags }}'
+          CPPFLAGS: '${{ matrix.cppflags }}'
           MATRIX_CHKPREFILL: '${{ matrix.chkprefill }}'
           MATRIX_CONFIG: '${{ matrix.config }}'
           MATRIX_ENV: '${{ matrix.env }}'
@@ -309,7 +309,7 @@ jobs:
           TFLAGS: '${{ matrix.tflags }}'
         run: |
           if [ "${MATRIX_TEST}" = 'uwp' ]; then
-            CPPFLAGS='-DWINSTORECOMPAT -DWINAPI_FAMILY=WINAPI_FAMILY_APP'
+            CPPFLAGS+=' -DWINSTORECOMPAT -DWINAPI_FAMILY=WINAPI_FAMILY_APP'
             if [[ "${MATRIX_ENV}" != 'clang'* ]]; then
               specs="$(realpath gcc-specs-uwp)"
               gcc -dumpspecs | sed -e 's/-lmingwex/-lwindowsapp -lmingwex -lwindowsapp/' -e 's/-lmsvcrt/-lucrtapp/' > "${specs}"
@@ -341,7 +341,7 @@ jobs:
               false
             fi
           else
-            export CFLAGS CPPFLAGS
+            export CFLAGS
             mkdir bld && cd bld && ../configure --prefix="$HOME"/curl-install --enable-unity --enable-warnings --enable-werror --disable-static \
               --disable-dependency-tracking --enable-option-checking=fatal \
               --with-libssh2 \