Cygwin: use absolute path with cygpath conversion to the linker script again

because the relative path is interpreted differently on linux, mac and windows

cmake/cygwin_cygpath.cmake

+############################################################################
+#
+# Copyright (c) 2017 PX4 Development Team. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in
+#    the documentation and/or other materials provided with the
+#    distribution.
+# 3. Neither the name PX4 nor the names of its contributors may be
+#    used to endorse or promote products derived from this software
+#    without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+# OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+############################################################################
+
+#=============================================================================
+#
+#	Converts a cygwin path (/cygdrive/c/...) to a mixed windows path (C:/...)
+#
+#	It is called on every platform but only adjusts the output when
+#	called inside the cygwin environment.
+#
+
+macro (CYGPATH _path _cygpath)
+	if (CMAKE_HOST_SYSTEM_NAME STREQUAL CYGWIN)
+		EXECUTE_PROCESS(COMMAND cygpath.exe -m ${${_path}}
+		OUTPUT_VARIABLE ${_cygpath})
+		string (STRIP ${${_cygpath}} ${_cygpath})
+	else()
+		set(${_cygpath} ${${_path}})
+	endif ()
+endmacro (CYGPATH)

platforms/nuttx/CMakeLists.txt

 include(common/px4_upload)
+include(cygwin_cygpath)
 
 if (NOT FW_NAME)
 	set(FW_NAME ${CONFIG}.elf)
@@ -37,9 +38,13 @@ endif()
 
 file(RELATIVE_PATH PX4_BINARY_DIR_REL ${CMAKE_CURRENT_BINARY_DIR} ${PX4_BINARY_DIR})
 
+# only in the cygwin environment: convert absolute linker script path to mixed windows (C:/...)
+# because even relative linker script paths are different for linux, mac and windows
+CYGPATH(PX4_BINARY_DIR PX4_BINARY_DIR_CYG)
+
 target_link_libraries(${FW_NAME}
 
-	-Wl,--script=${PX4_BINARY_DIR_REL}/NuttX/nuttx/configs/${BOARD}/scripts/${LD_SCRIPT}
+	-Wl,--script=${PX4_BINARY_DIR_CYG}/NuttX/nuttx/configs/${BOARD}/scripts/${LD_SCRIPT}
 	-Wl,-Map=${CONFIG}.map
 	-Wl,--warn-common,--gc-sections