configure: Move newlib libc check before mingw libc check

On Cygwin systems MinGW headers can be present if the corresponding
packages have been installed. Since the MinGW libc is checked for
first, this results in newlib getting misdetected as MinGW libc.

configure

@@ -3041,15 +3041,16 @@ if check_cpp_condition features.h "defined __UCLIBC__"; then
 elif check_cpp_condition features.h "defined __GLIBC__"; then
     libc_type=glibc
     add_cppflags -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600
+# MinGW headers can be installed on Cygwin, so check for newlib first.
+elif check_cpp_condition newlib.h "defined _NEWLIB_VERSION"; then
+    libc_type=newlib
+    add_cppflags -U__STRICT_ANSI__
 elif check_header _mingw.h; then
     libc_type=mingw
     check_cpp_condition _mingw.h \
         "defined (__MINGW64_VERSION_MAJOR) || (__MINGW32_MAJOR_VERSION > 3) || \
             (__MINGW32_MAJOR_VERSION == 3 && __MINGW32_MINOR_VERSION >= 15)" ||
         die "ERROR: MinGW runtime version must be >= 3.15."
-elif check_cpp_condition newlib.h "defined _NEWLIB_VERSION"; then
-    libc_type=newlib
-    add_cppflags -U__STRICT_ANSI__
 elif check_func_headers stdlib.h _get_doserrno; then
     libc_type=msvcrt
     add_compat strtod.o strtod=avpriv_strtod