latent_entropy: avoid build error when plugin cflags are not set

Some architectures set up CFLAGS for linux decompressor phase from scratch and do not include GCC_PLUGINS_CFLAGS. Since "latent_entropy" variable declaration is generated by the plugin code itself including linux/random.h in decompressor code then would cause a build error. E.g. on s390: In file included from ./include/linux/net.h:22, from ./include/linux/skbuff.h:29, from ./include/linux/if_ether.h:23, from ./arch/s390/include/asm/diag.h:12, from arch/s390/boot/startup.c:8: ./include/linux/random.h: In function 'add_latent_entropy': ./include/linux/random.h:26:39: error: 'latent_entropy' undeclared (first use in this function); did you mean 'add_latent_entropy'? 26 | add_device_randomness((const void *)&latent_entropy, | ^~~~~~~~~~~~~~ | add_latent_entropy ./include/linux/random.h:26:39: note: each undeclared identifier is reported only once for each function it appears in The build error is triggered by commit a80313ff91ab ("s390/kernel: introduce .dma sections") which made it into 5.2 merge window. To address that avoid using CONFIG_GCC_PLUGIN_LATENT_ENTROPY in favour of LATENT_ENTROPY_PLUGIN definition which is defined as a part of gcc plugins cflags and hence reflect more accurately when gcc plugin is active. Besides that it is also used for similar purpose in linux/compiler-gcc.h for latent_entropy attribute definition.

VGVasily Gorbik committed 7 years ago