search-paths: Allow specs with #f as their separator.

This adds support for single-entry search paths.
Fixes <http://bugs.gnu.org/25422>.
Reported by Leo Famulari <leo@famulari.name>.

* guix/search-paths.scm (<search-path-specification>)[separator]:
Document as string or #f.
(evaluate-search-paths): Add case for SEPARATOR as #f.
(environment-variable-definition): Handle SEPARATOR being #f.
* guix/build/utils.scm (list->search-path-as-string): Add case for
SEPARATOR as #f.
(search-path-as-string->list): Likewise.
* guix/build/profiles.scm (abstract-profile): Likewise.
* tests/search-paths.scm: New file.
* Makefile.am (SCM_TESTS): Add it.
* tests/packages.scm ("--search-paths with single-item search path"):
New test.
* gnu/packages/version-control.scm (git)[native-search-paths](separator):
New field.

guix package: Honor the order of profiles when -p appears multiple times.

* guix/scripts/package.scm (process-query): Reverse the order of
PROFILES.
* tests/guix-package-net.sh: Test it with '--search-paths'.

gnu: openssl: Don't replace 'sh' reference with 'bash'.

* gnu/packages/tls.scm (openssl)[arguments]: Use /bin/sh instead of /bin/bash in
'patch-tests' phase.

gnu: mit-krb5: Don't replace 'sh' reference with 'bash'.

* gnu/packages/mit-krb5.scm (mit-krb5)[arguments]: Use /bin/sh instead of
/bin/bash in 'pre-check' phase.

gnu: ghostscript: Don't replace 'sh' reference with 'bash'.

* gnu/packages/ghostscript.scm (ghostscript)[arguments]: Use /bin/sh instead of
/bin/bash in 'patch-config-files' phase.

gnu: attr: Don't replace 'sh' reference with 'bash'.

* gnu/packages/attr.scm (attr)[arguments]: Use /bin/sh instead of /bin/bash in
'check' phase.

gnu: gcc@5: Respect SOURCE_DATE_EPOCH in __DATE__ and __TIME__ macros.

* gnu/packages/patches/gcc-5-source-date-epoch-1.patch,
  gnu/packages/patches/gcc-5-source-date-epoch-2.patch: New files.
* gnu/local.mk (dist_patch_DATA): Register them.
* gnu/packages/gcc.scm (gcc-5)[source]: Use them.

gnu: Remove pcre-CVE-2016-3191.patch.

This is a follow-up to 026ee1a5a669658c8d4745c2733b4c201ca0e48e.

* gnu/packages/patches/pcre-CVE-2016-3191.patch: Delete file.
* gnu/local.mk (dist_patch_DATA): Remove it.

gnu: pcre: Update to 8.40.

* gnu/packages/pcre.scm (pcre): Update to 8.40.
[source]: Remove obsolete patch 'pcre-CVE-2016-3191.patch'.

gnu: gcc: Properly set the dynamic linker file name on GNU/Hurd.

* gnu/packages/gcc.scm (gcc-4.7)[arguments]: In 'pre-configure' phase,
match 'GNU_USER_DYNAMIC_LINKER' in addition to 'GLIBC_DYNAMIC_LINKER'.
This fixes GNU/Hurd cross-compilation as reported at
<https://lists.gnu.org/archive/html/guix-devel/2017-01/msg01731.html>.

gnu: sed: Do not attempt to rebuild 'doc/sed.1'.

* gnu/packages/base.scm (sed)[arguments]: Add 'dont-rebuild-sed.1'
phase.
[native-inputs]: Remove.

gnu: sed: Use the same phases whether or not we're cross-compiling.

* gnu/packages/base.scm (sed)[arguments]: Make #:phases argument
unconditional.  In 'patch-test-suite' phase, use (which "sh") instead of
referring to the "bash" input.

gnu: bash: Update to patch level 11.

* gnu/packages/bash.scm (%patch-series-4.4): Add patches 6 through 11.

gnu: ld-wrapper-boot0: Remove workaround for <http://bugs.gnu.org/24832>.

Fixes <http://bugs.gnu.org/24832>.

* gnu/packages/commencement.scm (ld-wrapper-boot0): Change the first
'make-ld-wrapper' argument to "ld-wrapper-boot0"; change #:target to
BOOT-TRIPLET.

hydra: Add "i586-pc-gnu" as a cross-compilation target.

* build-aux/hydra/gnu-system.scm (%cross-targets): Add "i586-pc-gnu".

gnu: tk: Update to 8.6.6.

* gnu/packages/tcl.scm (tk): Update to 8.6.6.

gnu: tcl: Update to 8.6.6.

* gnu/packages/tcl.scm (tcl): Update to 8.6.6.

gnu: zlib: Use 'modify-phases' syntax.

* gnu/packages/compression.scm (zlib)[arguments]: Use 'modify-phases'.

gnu: zlib: Update to 1.2.11.

* gnu/packages/compression.scm (zlib): Update to 1.2.11.

gnu: sqlite: Update to 3.16.2.

* gnu/packages/databases.scm (sqlite): Update to 3.16.2.