Remove more BUILD things

Signed-off-by: Graham MacDonald <grahamamacdonald@gmail.com>

amd64/clang-3.7.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-mno-implicit-float",
-]

amd64/clang-3.8.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-mno-implicit-float",
-]

amd64/clang-3.9.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-mno-implicit-float",
-]

amd64/clang.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-mno-implicit-float",
-]

amd64/gcc-4.8.BUILD

@@ -1,7 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-fno-pie",
-  "-fvar-tracking",
-  "-fvar-tracking-assignments"
-]

amd64/gcc-5.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-fno-pie",
-]

amd64/gcc-6.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-fno-pie",
-]

amd64/gcc.BUILD

@@ -1,7 +0,0 @@
-# Assumes gcc-4.8 is the default compiler for gcc.
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-fvar-tracking",
-  "-fvar-tracking-assignments"
-]

amd64/mkfile.clang

@@ -1,7 +0,0 @@
-
-</sys/src/mkfile.clang.proto
-
-CC=clang
-LD=clang
-O=o
-AS=clang

amd64/x86_64-elf-gcc.BUILD

@@ -1,5 +0,0 @@
-COMPILER_FLAGS=[
-  "-Wall",
-  "-Werror",
-  "-fno-pie",
-]