configure: expand path variables for meson configure

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -415,16 +415,7 @@ LDFLAGS_SHARED="-shared"
 modules="no"
 module_upgrades="no"
 prefix="/usr/local"
-mandir="\${prefix}/share/man"
-datadir="\${prefix}/share"
 firmwarepath="\${prefix}/share/qemu-firmware"
-qemu_docdir="\${prefix}/share/doc/qemu"
-bindir="\${prefix}/bin"
-libdir="\${prefix}/lib"
-libexecdir="\${prefix}/libexec"
-includedir="\${prefix}/include"
-sysconfdir="\${prefix}/etc"
-local_statedir="\${prefix}/var"
 confsuffix="/qemu"
 slirp=""
 oss_lib=""
@@ -979,12 +970,6 @@ if test "$mingw32" = "yes" ; then
     LIBS="-liberty $LIBS"
   fi
   prefix="c:/Program Files/QEMU"
-  mandir="\${prefix}"
-  datadir="\${prefix}"
-  qemu_docdir="\${prefix}"
-  bindir="\${prefix}"
-  sysconfdir="\${prefix}"
-  local_statedir=
   confsuffix=""
   libs_qga="-lws2_32 -lwinmm -lpowrprof -lwtsapi32 -lwininet -liphlpapi -lnetapi32 $libs_qga"
 fi
@@ -1638,6 +1623,26 @@ for opt do
   esac
 done
 
+libdir="${libdir:-$prefix/lib}"
+libexecdir="${libexecdir:-$prefix/libexec}"
+includedir="${includedir:-$prefix/include}"
+
+if test "$mingw32" = "yes" ; then
+    mandir="$prefix"
+    datadir="$prefix"
+    qemu_docdir="$prefix"
+    bindir="$prefix"
+    sysconfdir="$prefix"
+    local_statedir=
+else
+    mandir="${mandir:-$prefix/share/man}"
+    datadir="${datadir:-$prefix/share}"
+    qemu_docdir="${qemu_docdir:-$prefix/share/doc/qemu}"
+    bindir="${bindir:-$prefix/bin}"
+    sysconfdir="${sysconfdir:-$prefix/etc}"
+    local_statedir="${local_statedir:-$prefix/var}"
+fi
+
 case "$cpu" in
     ppc)
            CPU_CFLAGS="-m32"