[mingw] Some more tweaks

It now survives ./config.status --recheck as well.

https://github.com/harfbuzz/harfbuzz/issues/1728

mingw-configure.sh

@@ -8,22 +8,21 @@ esac
 target=$1-w64-mingw32
 shift
 
-unset CC
-unset CXX
-unset CPP
-unset LD
-unset LDFLAGS
-unset CFLAGS
-unset CXXFLAGS
-unset PKG_CONFIG_PATH
-
-# Removed -static from the following
-export CFLAGS="-static-libgcc"
-export CXXFLAGS="-static-libgcc -static-libstdc++"
-export CPPFLAGS="-I$HOME/.local/$target/include"
-export LDFLAGS=-L$HOME/.local/$target/lib
-export PKG_CONFIG_LIBDIR=$HOME/.local/$target/lib/pkgconfig:/usr/$target/sys-root/mingw/lib/pkgconfig/
-export PKG_CONFIG_PATH=$HOME/.local/$target/share/pkgconfig:/usr/$target/sys-root/mingw/share/pkgconfig/
-export PATH=$HOME/.local/$target/bin:/usr/$target/sys-root/mingw/bin:/usr/$target/bin:$PATH
-
-../configure --build=`../config.guess` --host=$target --prefix=$HOME/.local/$target --with-uniscribe --without-icu "$@"
+exec "$(dirname "$0")"/configure \
+	--build=`../config.guess` \
+	--host=$target \
+	--prefix=$HOME/.local/$target \
+	CC= \
+	CXX= \
+	CPP= \
+	LD= \
+	CFLAGS="-static-libgcc" \
+	CXXFLAGS="-static-libgcc -static-libstdc++" \
+	CPPFLAGS="-I$HOME/.local/$target/include" \
+	LDFLAGS=-L$HOME/.local/$target/lib \
+	PKG_CONFIG_LIBDIR=$HOME/.local/$target/lib/pkgconfig:/usr/$target/sys-root/mingw/lib/pkgconfig/ \
+	PKG_CONFIG_PATH=$HOME/.local/$target/share/pkgconfig:/usr/$target/sys-root/mingw/share/pkgconfig/ \
+	PATH=$HOME/.local/$target/bin:/usr/$target/sys-root/mingw/bin:/usr/$target/bin:$PATH \
+	--without-icu \
+	--with-uniscribe \
+	"$@"

mingw32.sh

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec "`dirname "$0"`/mingw-configure.sh" i686 "$@"
+exec "$(dirname "$0")"/mingw-configure.sh i686 "$@"

mingw64.sh

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec "`dirname "$0"`/mingw-configure.sh" x86_64 "$@"
+exec "$(dirname "$0")"/mingw-configure.sh x86_64 "$@"