Reduce number of sections in loader.elf

[nyh]

Right now, our loader.elf has more than 3000 (!) ELF sections (see bjdump -h build/release/loader.elf). All these sections subdivisions waste space (about half a megabyte), and the subdivision of the "text" sections causes "perf kvm"'s output to be unreadable.

The solution is to fix arch/x64/loader.ld
The most important part is to merge the .text.* sections. A patch for this would be (Avi already sent a similar patch):

-    .text : { *(.text) *(.text.hot) *(.text.unlikely) *(.text.fixup) } :text
+    .text : {
+        *(.text.hot .text.hot.*)
+        *(.text.unlikely .text.unlikely.* .text.*_unlikely)
+        *(.text.fixup)
+        *(.text.startup .text.startup.*)
+        *(.text .text._*)
+    } :text

There are also hundreds of data sections, the following patch correctly merges them:

-    .data : { *(.data) } :text
+/*    .data : { *(.data) } :text */
+    .data.rel.ro : {
+        *(.data.rel.ro.local* .gnu.linkonce.d.rel.ro.local.*)
+        *(.data.rel.ro .data.rel.ro.* .gnu.linkonce.d.rel.ro.*)
+    } : text
+    .data : { *(.data .data.* .gnu.linkonce.d.*) } :text

What remain are several hundred .gcc_except_table.* sections. An attempt to merge them with:

+    .gcc_except_table : { *(.gcc_except_table) *(.gcc_except_table.*) } : text

Miserably fails - the generated code hangs when using timers, I still have no idea why (most benchmarks fail, try for example tst-pipe.so).
Interestingly, if in the above line I replace "text" by "dynamic", I get a linker warning, but everything works (the sections are merged, and the resulting code appears to work). have no idea why.

[nyh]

The bug that caused timers to stop working when gcc_except_table sections are merged is gone - I am guessing this was an unrelated timer bug (see commits 870d841 and 9c3308f).

Merging the separate gcc_except_table shaves about 90K from our loader-stripped.elf