gcc generates .h.gch files even though there's no .h files in compiler

We're making a makefile for a class project, and we're having problems with gcc generating .h.gch files. Looked around on stack overflow and apparently it's normally caused by either including .h files in dependencies or having something like #include *.cpp, which we did not do in our make file.

We get this error when we compile, change a file and compile again. For now we can fix it with make clean before compiling again, but if possible we'd like to prevent the .h.gch file from being generated :

vr-gcc -I. -MMD  -g -mmcu=atmega324pa -Os -fpack-struct -fshort-enums -funsigned-bitfields -funsigned-char -Wall                                         -fno-exceptions      -c pwm.cpp pwm.h interruptNormal.h
cc1: warning: the "stabs" debug format cannot be used with pre-compiled headers [-Wdeprecated]
In file included from pwm.h:5:0:
interruptNormal.h:8:1: error: unknown type name 'class'
 class InterruptNormal{
 ^~~~~
interruptNormal.h:8:22: error: expected '=', ',', ';', 'asm' or '_attribute_' before '{' token
 class InterruptNormal{
                      ^
pwm.h:7:1: error: unknown type name 'class'
 class Pwm : public InterruptNormal{
 ^~~~~
pwm.h:7:11: error: expected '=', ',', ';', 'asm' or '_attribute_' before ':' token
 class Pwm : public InterruptNormal{
           ^
cc1: warning: the "stabs" debug format cannot be used with pre-compiled headers [-Wdeprecated]
interruptNormal.h:8:1: error: unknown type name 'class'
 class InterruptNormal{
 ^~~~~
interruptNormal.h:8:22: error: expected '=', ',', ';', 'asm' or '_attribute_' before '{' token
 class InterruptNormal{
                      ^
make: * [Makefile:146: pwm.o] Error 1

part of the makefile (not sure how much I could post since we'd like to avoid problems with plagiarism) :

PRJSRC= $(wildcard *.cpp)
CPPFILES=$(filter %.cpp, $(PRJSRC))
OBJDEPS=$(CPPFILES:.cpp=.o)

%.o: %.cpp
    $(CC) $(CFLAGS) $(CXXFLAGS) -c $^

%.hex: %.out
    $(OBJCOPY) -j .text -j .data \
        -O $(HEXFORMAT) $< $@

Thanks!