cmake interprets "\ " as End Of String? - cmake

Question

I'm trying to port my AtmelStudio build system into cmake. The following line of my CMakeLists.txt will fail when I make it. I placed the "" before " " so it would run but that doesn't seem to solve it.
SET(CINC -I"C:/Program\ Files\ (x86)/Atmel/Studio/7.0/Packs/atmel/ATmega_DFP/1.0.90/include")
...
SET(CFLAGS "${CMX} ${CMS} ${CPTH} ${CMCU} ${CDEBUG} ${CDEFS} ${CINC} ${COPT} ${CWARN} ${CSTANDARD} ${CEXTRA} ${CY}")
SET(CMAKE_C_FLAGS ${CFLAGS})
Make will print
C:\MinGW\bin\gcc.exe
-x c -MD;-MP;-MF;CMakeFiles/some_sequence.dir/a_util.c.obj;
-MT;CMakeFiles/some_sequence.dir/a_util.c.obj;-MT;
CMakeFiles/some_sequence.dir/a_util.c.obj
-B;C:/Program Files (x86)/Atmel/Studio/7.0/Packs/atmel/ATmega_DFP/1.0.90/gcc/dev/atmega644a
-mmcu=atmega644a -gstabs -DSOME_CONST -I;C:/Program Files (x86)/Atmel/Studio/7.0/Packs/atmel/ATmega_DFP/1.0.90/include
-Os -Wall -Wstrict-prototypes -std=gnu99 -c -MD -MT CMakeFiles/some_sequence.dir/a_util.c.obj -MF CMakeFiles\some_sequence.dir\a_util.c.obj.d -o
CMakeFiles\some_sequence.dir\a_util.c.obj -c C:\Projects\someboardfirmware\some_sequence\a_util.c
gcc.exe: error: Files: No such file or directory
gcc.exe: error: (x86)/Atmel/Studio/7.0/Packs/atmel/ATmega_DFP/1.0.90/gcc/dev/atmega644a: No such file or directory
It looks like it would interpret this line as if there were multiple strings but that doesn't make any sense to me... any idea?