Don't hassle with -march and -mtune, use gcc defaults.

diff --git a/Makefile-ponyc b/Makefile-ponyc
index 50f4936..8f28e1a 100644
--- a/Makefile-ponyc
+++ b/Makefile-ponyc
@@ -108,9 +108,9 @@ else
 endif
 
 LIB_EXT ?= a
-BUILD_FLAGS = -march=$(arch) -mtune=$(tune) -Werror -Wconversion \
+BUILD_FLAGS = -Werror -Wconversion \
   -Wno-sign-conversion -Wextra -Wall
-LINKER_FLAGS = -march=$(arch) -mtune=$(tune) $(LDFLAGS)
+LINKER_FLAGS = $(LDFLAGS)
 AR_FLAGS ?= rcs
 ALL_CFLAGS = -std=gnu11 -fexceptions \
   -DPONY_VERSION=\"$(tag)\" -DLLVM_VERSION=\"$(llvm_version)\" \
@@ -120,7 +120,7 @@ ALL_CFLAGS = -std=gnu11 -fexceptions \
   -DPONY_VERSION_STR=\"$(version_str)\" \
   -D_FILE_OFFSET_BITS=64
 ALL_CXXFLAGS = -std=gnu++11 -fno-rtti
-LL_FLAGS = -mcpu=$(cpu)
+LL_FLAGS =
 
 # Determine pointer size in bits.
 BITS := $(bits)
@@ -147,11 +147,6 @@
   endif
 endif
 
-ifneq ($(fpu),)
-  BUILD_FLAGS += -mfpu=$(fpu)
-  LINKER_FLAGS += -mfpu=$(fpu)
-endif
-
 ifdef link
   ifeq (,$(filter $(link),static llvm-static llvm-dynamic))
     $(error Unknown linking strategy "$(link)")