build: speed up kernel symbol export stripping

GNU grep has a high per-expression setup overhead when compiling regular
expressions. Use -F to force it to interpret the input as fixed strings,
which is much faster (fraction of a second instead of multiple minutes).

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 39049

include/kernel-build.mk

@@ -76,9 +76,9 @@ define BuildKernel
 		xargs $(TARGET_CROSS)nm | \
 		awk '$$$$1 == "U" { print $$$$2 } ' | \
 		sort -u > $(KERNEL_BUILD_DIR)/mod_symtab.txt
-	$(TARGET_CROSS)nm -n $(LINUX_DIR)/vmlinux.o | grep ' r __ksymtab' | sed -e 's,........ r __ksymtab_,,' > $(KERNEL_BUILD_DIR)/kernel_symtab.txt
-	grep -f $(KERNEL_BUILD_DIR)/mod_symtab.txt $(KERNEL_BUILD_DIR)/kernel_symtab.txt > $(KERNEL_BUILD_DIR)/sym_include.txt
-	grep -vf $(KERNEL_BUILD_DIR)/mod_symtab.txt $(KERNEL_BUILD_DIR)/kernel_symtab.txt > $(KERNEL_BUILD_DIR)/sym_exclude.txt
+	$(TARGET_CROSS)nm -n $(LINUX_DIR)/vmlinux.o | grep -F ' r __ksymtab' | sed -e 's,........ r __ksymtab_,,' > $(KERNEL_BUILD_DIR)/kernel_symtab.txt
+	grep -Ff $(KERNEL_BUILD_DIR)/mod_symtab.txt $(KERNEL_BUILD_DIR)/kernel_symtab.txt > $(KERNEL_BUILD_DIR)/sym_include.txt
+	grep -Fvf $(KERNEL_BUILD_DIR)/mod_symtab.txt $(KERNEL_BUILD_DIR)/kernel_symtab.txt > $(KERNEL_BUILD_DIR)/sym_exclude.txt
 	( \
 		echo '#define SYMTAB_KEEP \'; \
 		cat $(KERNEL_BUILD_DIR)/sym_include.txt | \