EFI: Remove SHARED=false usage by enforcing -no-undefined

We've been using SHARED=false to capture unported stuff. However it can be
captured using -no-undefined. This patch removes SHARED option and adds
-no-undefined. Original by Marcelo Ferreira <joamarcelo@gmail.com>,
Improved by Lv Zheng <lv.zheng@intel.com>

Signed-off-by: Marcelo Ferreira <joamarcelo@gmail.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>

generate/efi/Makefile.config

@@ -27,15 +27,6 @@
 # OPT_CFLAGS Optimization CFLAGS can be overridden on the make command
 #            line by adding the followings to the invocation:
 #            OPT_CFLAGS="..."
-# SHARED     Testing build to check if symbols are not implemented.
-#            GCC won't complain missing of symbols as our programs are
-#            compiled with -shared. This can be overridden on the make
-#            command line by adding the followings to the invocation:
-#            SHARED=false
-#            Link failures should only be seen for the _start and
-#            DivU64x32.  They are the only 2 GNU EFI functions we are
-#            using in order not to introduce architecture specific code
-#            into ACPICA.
 #
 # Notes:
 #   gcc should be version 4 or greater, otherwise some of the options
@@ -50,7 +41,6 @@
 PROGS =  acpidump
 HOST =   $(shell uname -m | sed s,i[3456789]86,ia32,)
 TARGET = $(shell uname -m | sed s,i[3456789]86,ia32,)
-SHARED ?= true
 OBJDIR = obj
 BINDIR = bin
 
@@ -108,13 +98,9 @@ CFLAGS  = \
 LDFLAGS	= \
 	-nostdlib\
 	-znocombreloc\
-	-Bsymbolic
-ifeq ($(strip $(SHARED)), true)
-LDFLAGS	+= \
-	-shared
-endif
-LIBS    = \
-	$(shell $(CC) -print-libgcc-file-name)
+	-Bsymbolic\
+	-shared\
+	-no-undefined
 OBJCOPYFLAGS = \
 	-j .text\
 	-j .sdata\
@@ -219,9 +205,10 @@ LDFLAGS	+= \
 	-T $(EFILIB)/elf_$(TARGET)_efi.lds\
 	-L$(EFILIB)\
 	$(EFILIB)/crt0-efi-$(TARGET).o
-LIBS += \
+LIBS = \
 	-lefi\
 	-lgnuefi\
+	$(shell $(CC) -print-libgcc-file-name)
 
 #
 # Bison/Flex configuration