请问这个makefile 文件前几行是什么意思，谢谢！
# THIS IS AN EXAMPLE FOR INTEL-LINUX PLATFORMS RUNNING PGF COMPILERS. CUSTOMIZE!
.SUFFIXES: .inc .f .F
MAKE = /usr/bin/make
CPP = /usr/bin/cpp -C -P $*.F > $*.f
FC = /usr/local/pgi/linux86/bin/pgf90 -Mfree
DEBUG = -tp p6 -O1 -Mnoframe -byteswapio -Mi4 -Mcache_align -Mdalign -pc 64
OFLAG = -tp p6 -O2 -Munroll -Mnoframe -byteswapio -Mi4 -Mcache_align -Mdalign -pc 64
DOUBLE = -r8
SINGLE =
TIMING =
#TIMING = -pg
