gem5: update to 7bfb7f3a43f382eb49853f47b140bfd6caad0fb8

The update is required to include 3c3ca64b5f0dd9eef7b1ce1c65cc6e8e9147dd38
otherwise baremetal does not on VExpress.

baremetal: create a baremetal setup with crosstool-ng

buildroot: improve directory location: move out/dl inside
out/buildroot/download, and add a new out/buildroot/build level

tagline: generalize, deliver more value than howto, since now howtos
are starting to multiply

rename all top scripts to separate words with hyphen more consistently,
e.g. run-gdb instead of rungdb

getvar: list all variables

gem5: make m5out section to focus all releated information at

Prevent m5term Text file busy when rebuilding gem5 while it is running.

baremetal/arch/arm/gem5_assert.S

@@ -0,0 +1,19 @@
+/* assert 0x12345678 + 1 == 0x12345679 */
+.global main
+main:
+    movw r0, #:lower16:myvar
+    movt r0, #:upper16:myvar
+    ldr r1, [r0]
+    add r1, r1, #1
+    str r1, [r0]
+    movw r2, #0x5679
+    movt r2, #0x1234
+    cmp r1, r2
+    beq ok
+    # m5 fail 1
+    mov r0, #0; mov r1, #0; mov r2, #1; mov r3, #0; .inst 0xEE000110 | (0x22 << 16);
+ok:
+    # m5 exit
+    mov r0, #0; mov r1, #0; .inst 0xEE000110 | (0x21 << 16);
+myvar:
+    .word 0x12345678

baremetal/arch/arm/no_bootloader/semihost_exit.S

@@ -0,0 +1,5 @@
+.global mystart
+mystart:
+    mov r0, #0x18
+    ldr r1, =#0x20026
+    svc 0x00123456

baremetal/arch/arm/semihost_exit.S

@@ -0,0 +1,5 @@
+.global main
+main:
+    mov r0, #0x18
+    ldr r1, =#0x20026
+    svc 0x00123456