Do more optimization for size

Some of the size optimizations from the first stage bootstrap leak into
the second stage itself. This means the distribution can be made slighly
smaller by optimizing for size in certain parts of the first stage.

Dockerfile

@@ -86,7 +86,10 @@ RUN /gcc-$GCC_VERSION/configure \
         --enable-version-specific-runtime-libs \
         --disable-dependency-tracking \
         --disable-nls \
-        --disable-multilib
+        --disable-multilib \
+        CFLAGS="-Os" \
+        CXXFLAGS="-Os" \
+        LDFLAGS="-s"
 RUN make -j$(nproc) all-gcc
 RUN make install-gcc
 
@@ -106,7 +109,9 @@ RUN /mingw-w64-v$MINGW_VERSION/mingw-w64-libraries/winpthreads/configure \
         --with-sysroot=/bootstrap/x86_64-w64-mingw32 \
         --host=x86_64-w64-mingw32 \
         --enable-static \
-        --disable-shared
+        --disable-shared \
+        CFLAGS="-Os" \
+        LDFLAGS="-s"
 RUN make -j$(nproc)
 RUN make install
 
@@ -231,7 +236,9 @@ RUN /mingw-w64-v$MINGW_VERSION/mingw-w64-libraries/winpthreads/configure \
         --with-sysroot=$PREFIX/x86_64-w64-mingw32 \
         --host=x86_64-w64-mingw32 \
         --enable-static \
-        --disable-shared
+        --disable-shared \
+        CFLAGS="-Os" \
+        LDFLAGS="-s"
 RUN make -j$(nproc)
 RUN make install